As filed with the Securities and Exchange Commission on May 2, 2022

Registration No. 333-                

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549

FORM S-3

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

CECO ENVIRONMENTAL CORP.

(Exact name of registrant as specified in its charter)

14651 North Dallas Parkway, Suite 500

Dallas, Texas 75254

Phone: (214) 357-6181

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Matthew Eckl

Chief Financial Officer

CECO Environmental Corp.

14651 North Dallas Parkway, Suite 500

Dallas, Texas 75254

Telephone: (214) 357-6181

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Bryan K. Brown

Amy S. Chen

Jones Day

717 Texas Avenue, Suite 3300

Houston, Texas 77002

Phone: (832) 239-3939

Fax: (832) 239-3600

Approximate date of commencement of proposed sale to the public: From time to time after this registration statement becomes effective.

If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box:  ☐

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box.  ☒

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ☐

If this Form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box.  ☐

If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box.  ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act.  ☐

The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the Registration Statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

The information in this prospectus is not complete and may be changed. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

SUBJECT TO COMPLETION, DATED MAY 2, 2022

Prospectus

CECO Environmental Corp.

$150,000,000

Common Stock

Preferred Stock

Depositary Shares

Warrants

Subscription Rights

Debt Securities

Purchase Contracts

Units

We may offer and sell from time to time our common stock, preferred stock, depositary shares, warrants, subscription rights, debt securities and purchase contracts, as well as units that include any of these securities. We may sell any combination of these securities in one or more offerings.

We will provide the specific terms of the securities to be offered in one or more supplements to this prospectus. You should read this prospectus and the applicable prospectus supplement carefully before you invest in our securities. This prospectus may not be used to offer and sell our securities unless accompanied by a prospectus supplement describing the method and terms of the offering of those securities.

We may sell the securities directly or to or through underwriters or dealers, and also to other purchasers or through agents. The names of any underwriters or agents that are included in a sale of securities to you, and any applicable commissions or discounts, will be stated in an accompanying prospectus supplement.

Our common stock is listed on the NASDAQ Stock Market under the symbol “CECE.” On April 29, 2022, the closing price of our common stock on the NASDAQ Stock Market was $4.75 per share. None of the other securities that we may offer under this prospectus are currently publicly traded.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is                , 2022.

Table of Contents

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About This Prospectus

This prospectus is part of a registration statement that we filed with the Securities and Exchange Commission, or the SEC, using a “shelf” registration process. Under this shelf process, we may from time to time sell any combination of the securities described in this prospectus in one or more offerings.

This prospectus provides you with a general description of the securities we may offer. Each time we sell securities, we will provide a prospectus supplement that will contain specific information about the terms of that offering. For a more complete understanding of the offering of the securities, you should refer to the registration statement, including its exhibits. The prospectus supplement may also add, update or change information contained in this prospectus. You should read both this prospectus and any prospectus supplement together with additional information under the heading “Where You Can Find More Information” and “Information We Incorporate By Reference.”

We have not authorized anyone to provide you with different information from the information contained or incorporated by reference in this prospectus and in any prospectus supplement or in any free writing prospectus that we may provide you. You should not assume that the information contained in this prospectus, any prospectus supplement, any document incorporated by reference or any free writing prospectus is accurate as of any date, other than the date mentioned on the cover page of these documents. We are not making offers to sell the securities in any jurisdiction in which an offer or solicitation is not authorized or in which the person making such offer or solicitation is not qualified to do so or to anyone to whom it is unlawful to make an offer or solicitation.

Unless we otherwise state or the context otherwise indicates, all references in this prospectus to “CECO,” “us,” “our,” or “we” mean CECO Environmental Corp. and its consolidated subsidiaries.

Where You Can Find More Information

We are subject to the information and periodic reporting requirements of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). We file annual, quarterly and current reports, proxy statements and other information with the SEC. Our SEC filings are available at the SEC’s website at http://www.sec.gov. You may also inspect our SEC reports and other information at our website at http://www.cecoenviro.com as soon as reasonably practicable after we electronically file such materials with, or furnish them to, the SEC. The information contained on or accessible through our website is not a part of this prospectus, other than the documents that we file with the SEC that are expressly incorporated by reference into this prospectus.

Information We Incorporate By Reference

The SEC allows us to “incorporate by reference” into this prospectus the information in documents we file with it, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be a part of this prospectus, and information that we file later with the SEC will automatically update and supersede this information. Any statement contained in any document incorporated or deemed to be incorporated by reference herein shall be deemed to be modified or superseded for purposes of this prospectus to the extent that a statement contained in or omitted from this prospectus or any accompanying prospectus supplement, or in any other subsequently filed document that also is or is deemed to be incorporated by reference herein, modifies or supersedes such statement. Any such statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this prospectus.

We incorporate by reference the documents listed below and any future documents that we file with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act (1) after the date of the initial filing of the

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registration statement of which this prospectus forms a part prior to the effectiveness of the registration statement and (2) after the date of this prospectus until the offering of the securities is terminated:

We will not, however, incorporate by reference in this prospectus any documents or portions thereof that are not deemed “filed” with the SEC, including any information furnished pursuant to Item 2.02 or Item 7.01 of our current reports on Form 8-K unless, and except to the extent, specified in such current reports.

We will provide you with a copy of any of these filings (other than an exhibit to these filings, unless the exhibit is specifically incorporated by reference into the filing requested) at no cost, if you submit a request to us by writing or telephoning us at the following address and telephone number:

CECO Environmental Corp.

14651 North Dallas Parkway, Suite 500

Dallas, Texas 75254

(888) 990-6670

Attention: Investor Relations

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The Company

CECO is a leading environmentally focused, diversified industrial company whose solutions protect people, the environment, and industrial equipment. We focus on engineering, designing, building, and installing systems that capture, clean and destroy air- and water-borne emissions from industrial facilities as well as fluid handling, gas separation, and filtration systems. CECO provides innovative technology and application expertise that helps companies grow their businesses with safe, clean, and more efficient solutions to protect our shared environment.

CECO serves diverse industries globally by working to improve air and water quality, protect customer’s equipment, and provide customized engineered solutions in our customers’ mission critical applications. The industries CECO serves include power generation, petrochemical processing, general industrial, refining, midstream oil & gas, electric vehicle production, poly silicon fabrication, battery recycling, and wastewater treatment, along with a wide range of other industries.

We operate through two reportable segments, as follows:

Corporate Information

CECO is a Delaware corporation and has been publicly traded since January 1, 1978. Our common stock trades on the NASDAQ Stock Market under the symbol “CECE.” Our principal executive offices are located at 14651 North Dallas Parkway, Suite 500, Dallas, Texas 75254. Our telephone number is (214) 357-6181. Our website is http://www.cecoenviro.com. The information contained on or accessible through our website is not part of this prospectus, other than the documents that we file with the SEC that are expressly incorporated by reference into this prospectus.

Risk Factors

Investment in any securities offered pursuant to this prospectus and the applicable prospectus supplement involves risks. You should carefully consider the risk factors incorporated by reference to our most recent Annual Report on Form 10-K, and any subsequent Quarterly Reports on Form 10-Q or Current Reports on Form 8-K, and all other information contained or incorporated by reference into this prospectus, as updated by our subsequent filings under the Exchange Act, and the risk factors and other information contained in the applicable prospectus supplement and any applicable free writing prospectus before acquiring any of such securities. The risks and uncertainties we have described are not the only ones facing our company. Additional risks and uncertainties not presently known to us or that we currently deem immaterial may also affect our business operations. The occurrence of any of these risks might cause you to lose all or part of your investment in the offered securities. The discussion of risks includes or refers to forward-looking statements. You should read the explanation of the qualifications and limitations on such forward-looking statements contained or incorporated by reference into this prospectus and in any applicable prospectus supplement.

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Disclosure Regarding Forward-Looking Statements

This prospectus, including the documents incorporated by reference, contains, and any prospectus supplement may contain, “forward-looking statements” as defined in the Private Securities Litigation Reform Act of 1995. Forward-looking statements speak only as of the date they are made and give our current expectations or forecasts of future events. These forward-looking statements can be identified by the use of forward-looking words, such as “anticipate,” “believe,” “estimate,” “expect,” “forecast,” “goal,” “intend,” “plan,” “predict,” “project,” “seek,” “target,” “could,” “may,” “should” or “would” or other similar expressions that convey the uncertainty of future events or outcomes. When we discuss our strategies and/or plans, we are making projections, forecasts or forward-looking statements. Such statements are based on the beliefs of, as well as assumptions made by and information currently available to, our management. While management believes that these forward-looking statements are reasonable as and when made, there can be no assurance that future developments affecting us will be those that we anticipate.

All of our forward-looking statements involve risks and uncertainties (some of which are significant or beyond our control) and assumptions that could cause actual results to differ materially from our historical experience and our present expectations or projections. Potential risks and uncertainties, among others, that could cause actual results to differ materially include, but are not limited to:

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Many of these risks are beyond management’s ability to control or predict. Should one or more of these risks or uncertainties materialize, or should the assumptions prove incorrect, actual results may vary in material aspects from those currently anticipated.

We disclose important factors that could cause our actual results to differ materially from our expectations implied by our forward-looking statements under “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” of the documents we incorporate by reference. These cautionary statements qualify all forward-looking statements attributed to us or persons acting on our behalf. When we indicate that an event, condition or circumstance could or would have an adverse effect on us, we mean to include effects upon our business, financial and other condition, results of operations, prospects and ability to service our debt.

The cautionary statements set forth above should be considered in connection with any subsequent written or oral forward-looking statements that we or persons acting on our behalf may issue. We caution readers not to place undue reliance on the statements, which speak only as of the date of this prospectus. We do not undertake any obligation to update or revise any forward-looking statement to reflect any changes in our expectations or any change in events, conditions, or circumstances on which any statement is based, except as may be required under applicable law.

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Use of Proceeds

Unless we inform you otherwise in the applicable prospectus supplement, we expect to use the net proceeds from the sale of securities for general corporate purposes. These purposes may include, but are not limited to:

Pending any specific application, we may initially invest funds in short-term marketable securities or apply them to the reduction of short-term indebtedness.

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Description of Capital Stock

Introduction

In the discussion that follows, we have summarized selected provisions of our certificate of incorporation and bylaws relating to our capital stock. This summary is not complete. This discussion is qualified in its entirety by reference to our certificate of incorporation and bylaws. You should read the provisions of our certificate of incorporation and bylaws as currently in effect for provisions that may be important to you. We have filed copies of those documents with the SEC, and they are incorporated by reference as exhibits to the registration statement of which this prospectus forms a part. See “Information We Incorporate By Reference.”

Authorized Capital Stock

Our authorized capital stock consists of:

Common Stock

Holders of our common stock are entitled to one vote for each share held on all matters submitted to a vote of our stockholders and do not have cumulative voting rights. Holders of a majority of the shares of common stock entitled to vote in any election of our directors may elect all of the directors standing for election. Holders of our common stock are entitled to receive ratably such dividends, if any, as may be declared by our board of directors out of funds legally available therefor, subject to any preferential dividend rights of outstanding preferred stock. Upon our liquidation, dissolution or winding up, the holders of common stock are entitled to receive ratably our net assets available after the payment of all debts and other liabilities and subject to the prior rights of any outstanding preferred stock. Holders of our common stock have no preemptive, subscription, redemption or conversion rights.

The outstanding shares of our common stock are fully paid and non-assessable.

The rights, preferences and privileges of holders of our common stock are subject to, and may be adversely affected by, the rights of the holders of shares of any series of preferred stock which we may designate and issue.

Preferred Stock

We have no outstanding shares of preferred stock. Our board of directors, without further action by our stockholders, is authorized to issue an aggregate of 10,000 shares of preferred stock. Our board of directors may issue preferred stock with dividend rates, redemption prices, preferences on liquidation or dissolution, conversion rights, voting rights and any other preferences, which rights and preferences could adversely affect the voting power of the holders of common stock. The issuance of preferred stock, while providing desirable flexibility in connection with possible acquisitions or other corporate purposes, could have the effect of making it more difficult for a third party to acquire us, or could discourage or delay a third party from acquiring control of us.

Limitation on Directors’ Liability

Pursuant to the provisions of the General Corporation Law of the State of Delaware (“DGCL”), we have adopted provisions in our certificate of incorporation and bylaws that require us to indemnify our officers and directors to the fullest extent permitted by law, and eliminate the personal liability of our directors to us or our stockholders for monetary damages for breach of their duty of due care except (a) for any breach of the directors’ duty of loyalty to the corporation or its stockholders, (b) for acts or omissions not in good faith or which involve intentional misconduct or a knowing violation of law, (c) for acts relating to unlawful payment of a dividend or

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an unlawful stock purchase or redemption or (d) for any transaction from which the director derived an improper personal benefit. These provisions do not eliminate a director’s duty of care. Moreover, the provisions do not apply to claims against a director for violation of certain laws, including federal securities laws. We believe that these provisions will assist it in attracting or retaining qualified individuals to serve as directors and officers.

Our certificate of incorporation and bylaws provide for mandatory indemnification of officers and directors of the corporation, including a director or officer of the corporation who is serving at the request of the corporation as a director, officer, employee or agent of another corporation, partnership, joint venture, trust or other enterprise, to the fullest extent permitted under the DGCL. We may also, at its discretion, provide the same benefits of indemnification to any employee or agent of the corporation.

Anti-Takeover Effects of Provisions of our Certificate of Incorporation and Bylaws

Some of the provisions of our certificate of incorporation and bylaws may have the effect of making it more difficult for a third party to acquire, or of discouraging a third party from attempting to acquire, control of us. These provisions are expected to discourage coercive takeover practices and inadequate takeover bids and to encourage persons seeking to acquire control of us to first negotiate with us. These provisions could limit the price investors might be willing to pay in the future for our common stock. We believe that the benefits of increased protection of our ability to negotiate with the proponent of an unfriendly or unsolicited acquisition proposal outweigh the disadvantage of discouraging these proposals, because among other things, negotiation may result in an improvement of their terms. These provisions could limit the price that investors might be willing to pay in the future for shares of our common stock. These provisions include:

In addition, subject to applicable limitations, our board of directors has the authority to issue up to 10,000 shares of preferred stock and to determine the price, rights, preferences, privileges and restrictions, including voting rights, of those shares without any further vote or action by the stockholders. The issuance of preferred stock, while providing flexibility in connection with possible financings or acquisitions or other corporate purposes, could have the effect of making it more difficult for a third party to acquire a majority of our outstanding voting stock. These and other provisions contained in our certificate of incorporation and bylaws could have the effect of delaying or preventing a change in control.

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Description of Depositary Shares

We may offer depositary shares representing fractional shares of our preferred stock of any series. The following description sets forth certain general terms and provisions of the depositary shares that we may offer pursuant to this prospectus. The particular terms of the depositary shares, including the fraction of a preferred share that such depositary share will represent, and the extent, if any, to which the general terms and provisions may apply to the depositary shares so offered, will be described in the applicable prospectus supplement.

The shares of preferred stock represented by depositary shares will be deposited under a depositary agreement between us and a bank or trust company that meets certain requirements and is selected by us, which we refer to as the bank depositary. Each owner of a depositary share will be entitled to all the rights and preferences of the shares of preferred stock represented by the depositary share. The depositary shares will be evidenced by depositary receipts issued pursuant to the depositary agreement. Depositary receipts will be distributed to those persons purchasing the fractional shares of preferred stock in accordance with the terms of the offering. The deposit agreement will also contain provisions relating to the manner in which any subscription or similar rights we offer to holders of the preferred stock will be made available to the holders of depositary shares.

The following description is a general summary of some common provisions of a depositary agreement and the related depositary receipts. The description below and in any prospectus supplement does not include all of the terms of the depositary agreement and the related depositary receipts. Copies of the form of depositary agreement and the depositary receipts relating to any particular issue of depositary shares will be filed with the SEC each time we issue depositary shares, and you should read those documents for provisions that may be important to you. For more information on how you can obtain copies of the forms of the depositary agreement and the related depositary receipts, see “Where You Can Find More Information.”

Dividends and Other Distributions

If we pay a cash distribution or dividend on a series of preferred stock represented by depositary shares, the bank depositary will distribute these dividends to the record holders of these depositary shares. If the distributions are in property other than cash, the bank depositary will distribute the property to the record holders of the depositary shares. However, if the bank depositary determines that it is not feasible to make the distribution of property, the bank depositary may, with our approval, sell this property and distribute the net proceeds from this sale to the record holders of the depositary shares.

Redemption of Depositary Shares

If we redeem a series of preferred stock represented by depositary shares, the bank depositary will redeem the depositary shares from the proceeds received by the bank depositary in connection with the redemption. The redemption price per depositary share will equal the applicable fraction of the redemption price per share of the preferred stock. If fewer than all the depositary shares are redeemed, the depositary shares to be redeemed will be selected by lot or pro rata as the bank depositary may determine.

Voting the Preferred Stock

Upon receipt of notice of any meeting at which the holders of the preferred stock represented by depositary shares are entitled to vote, the bank depositary will mail the notice to the record holders of the depositary shares relating to the preferred stock. Each record holder of these depositary shares on the record date (which will be the same date as the record date for the preferred stock) may instruct the bank depositary as to how to vote the preferred stock represented by this holder’s depositary shares. The bank depositary will endeavor, insofar as practicable, to vote the amount of the preferred stock represented by such depositary shares in accordance with these instructions, and we will take all action which the bank depositary deems necessary in order to enable the bank depositary to do so. The bank depositary will abstain from voting shares of the preferred stock to the extent it does not receive specific instructions from the holders of depositary shares representing this preferred stock.

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Amendment and Termination of the Depositary Agreement

The form of depositary receipt evidencing the depositary shares and any provision of the depositary agreement may be amended by agreement between the bank depositary and us. However, any amendment that materially and adversely alters the rights of the holders of depositary shares will not be effective unless this amendment has been approved by the holders of at least a majority of the depositary shares then outstanding. The depositary agreement may be terminated by the bank depositary or us only if:

Charges of Bank Depositary

We will pay all transfer and other taxes and governmental charges arising solely from the existence of the depositary arrangements. We will pay charges of the bank depositary in connection with the initial deposit of the preferred stock and any redemption of the preferred stock. Holders of depositary receipts will pay other transfer and other taxes and governmental charges and any other charges, including a fee for the withdrawal of shares of preferred stock upon surrender of depositary receipts, as are expressly provided in the depositary agreement to be for their accounts.

Withdrawal of Preferred Stock

Except as may be provided otherwise in the applicable prospectus supplement, upon surrender of depositary receipts at the principal office of the bank depositary, subject to the terms of the depositary agreement, the owner of the depositary shares may demand delivery of the number of whole shares of preferred stock and all money and other property, if any, represented by those depositary shares. Fractional shares of preferred stock will not be issued. If the depositary receipts delivered by the holder evidence a number of depositary shares in excess of the number of depositary shares representing the number of whole shares of preferred stock to be withdrawn, the bank depositary will deliver to this holder at the same time a new depositary receipt evidencing the excess number of depositary shares. Holders of preferred stock thus withdrawn may not thereafter deposit those shares under the depositary agreement or receive depositary receipts evidencing depositary shares therefor.

Miscellaneous

The bank depositary will forward to holders of depositary receipts all reports and communications from us that are delivered to the bank depositary and that we are required to furnish to the holders of preferred stock.

Neither the bank depositary nor we will be liable if we are prevented or delayed by law or any circumstance beyond our control in performing our obligations under the depositary agreement. The obligations of the bank depositary and us under the depositary agreement will be limited to performance in good faith of our duties thereunder, and we will not be obligated to prosecute or defend any legal proceeding in respect of any depositary shares or shares of preferred stock unless satisfactory indemnity is furnished. We may rely upon written advice of counsel or accountants, or upon information provided by persons presenting shares of preferred stock for deposit, holders of depositary receipts or other persons believed to be competent and on documents believed to be genuine.

Resignation and Removal of Bank Depositary

The bank depositary may resign at any time by delivering to us notice of its election to do so, and we may at any time remove the bank depositary. Any such resignation or removal will take effect upon the appointment of a successor bank depositary and the successor’s acceptance of this appointment. The successor bank depositary must be appointed within 60 days after delivery of the notice of resignation or removal and must be a bank or trust company meeting the requirements of the depositary agreement.

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Description of Warrants

We may issue warrants for the purchase of common stock, preferred stock, depositary shares or debt securities. The following description sets forth certain general terms and provisions of the warrants that we may offer pursuant to this prospectus. The particular terms of the warrants and the extent, if any, to which the general terms and provisions may apply to the warrants so offered will be described in the applicable prospectus supplement.

Warrants may be issued independently or together with other securities and may be attached to or separate from any offered securities. Each series of warrants will be issued under a separate warrant agreement to be entered into between us and a bank or trust company, as warrant agent. The warrant agent will act solely as our agent in connection with the warrants and will not have any obligation or relationship of agency or trust for or with any holders or beneficial owners of warrants.

A copy of the forms of the warrant agreement and the warrant certificate relating to any particular issue of warrants will be filed with the SEC each time we issue warrants, and you should read those documents for provisions that may be important to you. For more information on how you can obtain copies of the forms of the warrant agreement and the related warrant certificate, see “Where You Can Find More Information.”

Debt Warrants

The prospectus supplement relating to a particular issue of warrants to issue debt securities will describe the terms of those warrants, including the following:

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Stock Warrants

The prospectus supplement relating to a particular issue of warrants to issue common stock, preferred stock or depositary shares will describe the terms of the common stock warrants and preferred stock warrants, including the following:

Exercise of Warrants

Each warrant will entitle the holder of the warrant to purchase at the exercise price set forth in the applicable prospectus supplement the number of shares of common stock, preferred stock or depositary shares or the principal amount of debt securities being offered. Holders may exercise warrants at any time up to the close of business on the expiration date set forth in the applicable prospectus supplement. After the close of business on the expiration date, unexercised warrants are void. Holders may exercise warrants as set forth in the prospectus supplement relating to the warrants being offered.

Until a holder exercises the warrants to purchase our common stock, preferred stock, depositary shares or debt securities, the holder will not have any rights as a holder of our common stock, preferred stock, depositary shares or debt securities, as the case may be, by virtue of ownership of warrants.

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Description of Subscription Rights

We may issue to our stockholders subscription rights to purchase our common stock, preferred stock, depositary shares or debt securities. The following description sets forth certain general terms and provisions of the subscription rights that we may offer pursuant to this prospectus. The particular terms of the subscription rights and the extent, if any, to which the general terms and provisions may apply to the subscription rights so offered will be described in the applicable prospectus supplement.

Subscription rights may be issued independently or together with any other security offered by this prospectus and may or may not be transferable by the stockholder receiving the rights in the rights offering. In connection with any rights offering, we may enter into a standby underwriting agreement with one or more underwriters pursuant to which the underwriter will purchase any securities that remain unsubscribed for upon completion of the rights offering, or offer these securities to other parties who are not our stockholders. A copy of the form of subscription rights certificate will be filed with the SEC each time we issue subscription rights, and you should read that document for provisions that may be important to you. For more information on how you can obtain a copy of any subscription rights certificate, see “Where You Can Find More Information.”

The applicable prospectus supplement relating to any subscription rights will describe the terms of the offered subscription rights, including, where applicable, the following:

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Description of Debt Securities

The following description sets forth certain general terms and provisions of the debt securities that we may issue, which may be issued as convertible or exchangeable debt securities. We will set forth the particular terms of the debt securities we offer in a prospectus supplement and the extent, if any, to which the following general terms and provisions will apply to particular debt securities.

The debt securities will be issued under an indenture to be entered into between us and Wilmington Trust, National Association, as trustee. The indenture, and any supplemental indentures thereto, will be subject to, and governed by, the Trust Indenture Act of 1939, as amended. The following description of general terms and provisions relating to the debt securities and the indenture under which the debt securities may be issued is a summary only and therefore is not complete and is subject to, and qualified in its entirety by reference to, the terms and provisions of the indenture. The form of the indenture has been filed with the SEC as an exhibit to the registration statement, of which this prospectus forms a part, and you should read the indenture for provisions that may be important to you. For more information on how you can obtain a copy of the form of the indenture, see “Where You Can Find More Information.”

General

Unless otherwise specified in a prospectus supplement, the debt securities will be our direct, unsecured obligations and will rank equally with all of our existing and future senior unsecured indebtedness senior in right of payment to all of our subordinated indebtedness.

The indenture does not limit the aggregate principal amount of debt securities that may be issued under it and provides that debt securities may be issued under it from time to time in one or more series. We may specify a maximum aggregate principal amount for the debt securities of any series.

Unless otherwise specified in the applicable prospectus supplement, the indenture does not afford the holders of the debt securities the right to require us to repurchase or redeem the debt securities in the event of a highly-leveraged transaction.

We are not obligated to issue all debt securities of one series at the same time and, unless otherwise provided in the applicable prospectus supplement, we may reopen a series, without the consent of the holders of the outstanding debt securities of that series, for the issuance of additional debt securities of that series. Additional debt securities of a particular series will have the same terms and conditions as outstanding debt securities of such series, except for the issue date and, in some cases, the public offering price and the first interest payment date, and will be consolidated with, and form a single series with, such outstanding debt securities; provided, however, that if such additional debt securities are not fungible with the outstanding debt securities of such series for U.S. federal income tax purposes, the additional debt securities will have a separate CUSIP number.

We will set forth in a prospectus supplement relating to any debt securities being offered, the aggregate principal amount and the following terms of the debt securities, if applicable:

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The foregoing is not intended to be an exclusive list of the terms that may be applicable to any offered debt securities.

In addition, the indenture does not limit our ability to issue convertible, exchangeable or subordinated debt securities. Any conversion, exchange or subordination provisions of debt securities will be described in the relevant prospectus supplement. Such terms may include provisions for conversion or exchange, either mandatory, at the option of the holder or at our option, in which case the number of shares of common stock or other securities to be received by the holders of debt securities would be calculated as of a time and in the manner stated in the prospectus supplement.

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We may issue debt securities that provide for an amount less than their stated principal amount to be due and payable upon declaration of acceleration of their maturity pursuant to the terms of the indenture. We will provide you with information on the U.S. federal income tax considerations and other special considerations applicable to any of these debt securities in the applicable prospectus supplement.

If we denominate the purchase price of any of the debt securities in a foreign currency or currencies or a foreign currency unit or units, or if the principal of and any premium and interest on any series of debt securities is payable in a foreign currency or currencies or a foreign currency unit or units, we will provide you with information on the restrictions, elections, general tax considerations, specific terms and other information with respect to that issue of debt securities and such foreign currency or currencies or foreign currency unit or units in the applicable prospectus supplement.

Exchange and Transfer

Debt securities may be transferred or exchanged at the office of the registrar or co-registrar designated by us.

We will not impose a service charge for any transfer or exchange, but we may require holders to pay any tax or other governmental charges associated with any transfer or exchange.

In the event of any redemption of debt securities of any series, we will not be required to:

We may initially appoint the trustee as the registrar. Any transfer agent, in addition to the registrar initially designated by us, will be named in the prospectus supplement. We may designate additional transfer agents or change transfer agents or change the office of the transfer agent. However, we will be required to maintain a transfer agent in each place of payment for the debt securities of each series.

Global Securities

The debt securities of any series may be represented, in whole or in part, by one or more global securities. Each global security will:

No global security may be exchanged in whole or in part for debt securities registered in the name of any person other than the depositary or any nominee unless:

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As long as the depositary, or its nominee, is the registered owner of a global security, the depositary or nominee will be considered the sole owner and holder of the debt securities represented by the global security for all purposes under the indenture. Except in the above limited circumstances, owners of beneficial interests in a global security:

Payments on a global security will be made to the depositary or its nominee as the holder of the global security. Some jurisdictions have laws that require that certain purchasers of securities take physical delivery of such securities in definitive form. These laws may impair the ability to transfer beneficial interests in a global security.

Institutions that have accounts with the depositary or its nominee are referred to as “participants.” Ownership of beneficial interests in a global security will be limited to participants and to persons that may hold beneficial interests through participants. The depositary will credit, on its book-entry registration and transfer system, the respective principal amounts of debt securities represented by the global security to the accounts of its participants. Each person owning a beneficial interest in a global security must rely on the procedures of the depositary (and, if such person is not a participant, on procedures of the participant through which such person owns its interest) to exercise any rights of a holder under the indenture.

Ownership of beneficial interests in a global security will be shown on and effected through records maintained by the depositary, with respect to participants’ interests, or by any participant, with respect to interests of persons held by participants on their behalf. Payments, transfers and exchanges relating to beneficial interests in a global security will be subject to policies and procedures of the depositary. The depositary policies and procedures may change from time to time. Neither we nor the trustee will have any responsibility or liability for the depositary’s acts or omissions or any participant’s records with respect to beneficial interests in a global security.

Payment and Paying Agent

The provisions of this subsection will apply to the debt securities unless otherwise indicated in the prospectus supplement. Payment of interest on a debt security on any interest payment date will be made to the person in whose name the debt security is registered at the close of business on the regular record date. Payment on debt securities of a particular series will be payable at the office of a paying agent or paying agents designated by us. However, at our option, we may pay interest by mailing a check to the record holder.

We may also name any other paying agents in the prospectus supplement. We may designate additional paying agents, change paying agents or change the office of any paying agent. However, we will be required to maintain a paying agent in each place of payment for the debt securities of a particular series.

Subject to any applicable abandoned property law, all moneys paid by us to a paying agent for payment on any debt security that remain unclaimed at the end of two years after such payment was due will be repaid to us. Thereafter, the holder may look only to us for such payment.

Consolidation, Merger and Sale of Assets

Except as otherwise set forth in the applicable prospectus supplement, we may not merge or consolidate with or into any other person, in a transaction in which we are not the surviving corporation, or sell, convey,

17

transfer, lease or otherwise dispose of all or substantially all of the properties and assets of us and our subsidiaries, taken as a whole, to any person, unless:

In the event of the above transaction, if there is a successor or transferee, then the successor or transferee will expressly assume all of our obligations under the indenture and automatically be substituted for us in the indenture and as issuer of the debt securities and may exercise every right and power of ours under the indenture with the same effect as if such successor or transferee had been named in our place in the indenture; provided, however, that the predecessor company will not be relieved of the obligation to pay principal and interest on the debt securities except in the case of a sale of all of the assets of us and our subsidiaries.

Events of Default

Event of default means, with respect to any series of debt securities, any of the following:

We will promptly deliver to the trustee written notice of any event which with the giving of notice and the lapse of time would become a covenant event of default, or any other event of default provided with respect to debt securities of that series that is described in the applicable prospectus supplement, along with a description of the status and what action we are taking or propose to take with respect to such event of default.

No event of default with respect to a particular series of debt securities (except as to certain events of bankruptcy, insolvency or reorganization) necessarily constitutes an event of default with respect to any other

18

series of debt securities. The occurrence of an event of default may constitute an event of default under our bank credit agreements in existence from time to time. In addition, the occurrence of certain events of default or an acceleration under the indenture may constitute an event of default under certain of our other indebtedness outstanding from time to time.

If an event of default (other than an event of default resulting from certain events of bankruptcy, insolvency or reorganization of our company) with respect to debt securities of any series at the time outstanding occurs and is continuing, then the trustee or the holders of not less than 25% in aggregate principal amount of the outstanding debt securities of that series may, by a notice in writing to us (and to the trustee if given by the holders), declare to be due and payable immediately the principal (or, if the debt securities of that series are discount securities, that portion of the principal amount as may be specified in the terms of that series) of, and accrued and unpaid interest, if any, on all debt securities of that series. In the case of an event of default resulting from certain events of bankruptcy, insolvency or reorganization of our company, the principal (or such specified amount) of and accrued and unpaid interest, if any, on all outstanding debt securities will become and be immediately due and payable without any declaration or other act on the part of the trustee or any holder of outstanding debt securities. At any time after a declaration of acceleration with respect to debt securities of any series has been made, the holders of a majority in aggregate principal amount of the outstanding debt securities of that series may rescind and annul the acceleration if the rescission and annulment would not conflict with any judgment or decree already rendered and if all events of default with respect to that series, other than the non-payment of principal and interest, if any, with respect to debt securities of that series that has become due and payable solely because of the acceleration, have been cured or waived and all sums paid or advanced by the trustee and the reasonable compensation expenses and disbursements of the trustee and its agents and counsel have been paid as provided in the indenture.

The indenture provides that the trustee will be under no obligation to exercise any of its rights or powers under the indenture at the request of any holder of outstanding debt securities, unless the trustee receives security or indemnity satisfactory to it against any loss, liability or expense. Subject to certain rights of the trustee, the holders of a majority in principal amount of the outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee or exercising any trust or power conferred on the trustee with respect to the debt securities of that series.

No holder of any debt security of any series will have any right to institute any proceeding, judicial or otherwise, with respect to the indenture or for the appointment of a receiver or trustee, or for any remedy under the indenture, unless:

Notwithstanding the foregoing, the holder of any debt security will have an absolute and unconditional right to receive payment of the principal of, and premium and any interest on, that debt security on or after the due dates expressed in that debt security and to institute suit for the enforcement of such payment.

The indenture requires us, within 120 days after the end of our fiscal year, to furnish to the trustee a statement as to compliance with the indenture. The indenture provides that the trustee may withhold notice to the holders of debt securities of any series of any default or event of default (except in payment on any debt securities of that series) with respect to debt securities of that series if it in good faith determines that withholding notice is in the interest of the holders of those debt securities.

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Modification and Waiver

We may amend or modify the indenture without the consent of any holder of debt securities of the series affected by the modifications or amendments in order to:

Other amendments and modifications of the indenture or the debt securities issued may be made with the consent of the holders of at least a majority of the aggregate principal amount of the outstanding debt securities of the affected series, and our compliance with any provision of the indenture with respect to the debt securities may be waived by written notice to the trustee by the holders of a majority of the aggregate principal amount of the outstanding debt securities of the affected series. However, no modification or amendment may, without the consent of the holder of each outstanding debt security of the affected series:

Except for certain specified provisions, the holders of at least a majority in principal amount of the outstanding debt securities of an affected series may, on behalf of the holders of all debt securities of such series, waive our compliance with provisions of the indenture. Prior to the acceleration of the maturity of the debt securities of any series pursuant to the terms of the indenture, the holders of a majority in aggregate principal amount of the outstanding debt securities of such series may, on behalf of the holders of all the debt securities of

20

such series, waive any past default under the indenture with respect to such debt securities and its consequences, except (i) a default with respect to such series in the payment of the principal of, or premium or any interest on, the debt securities of such series or (ii) a default or event of default in respect of a covenant or provision that cannot be modified or amended without the consent of all of the holders of the outstanding debt securities of the affected series.

Defeasance of Debt Securities and Certain Covenants in Certain Circumstances

Legal Defeasance. The indenture provides that, in certain circumstances, we may be discharged from any and all obligations in respect of the debt securities of any series (except for certain obligations to register the transfer or exchange of debt securities, to replace stolen, lost or mutilated debt securities, and to maintain paying agencies and certain provisions relating to the treatment of funds held by paying agents). We will be so discharged upon the deposit with the trustee, in trust, of money and/or U.S. government obligations that, through the payment of interest and principal in accordance with their terms, will provide money in an amount sufficient in the written opinion of a nationally recognized firm of independent public accountants, a nationally recognized investment bank or a nationally recognized appraisal firm to pay and discharge each installment of principal, premium and interest in accordance with the terms of the indenture and the debt securities of that series.

This discharge may occur only if, among other things, we have delivered to the trustee an opinion of counsel stating that we have received from, or there has been published by, the United States Internal Revenue Service a ruling or, since the date of execution of the indenture, there has been a change in the applicable U.S. federal income tax law, in either case to the effect that, and based thereon such opinion shall confirm that, the beneficial owners of the debt securities of the applicable series will not recognize income, gain or loss for U.S. federal income tax purposes as a result of the deposit, defeasance and discharge and will be subject to U.S. federal income tax on the same amounts and in the same manner and at the same times as would have been the case if the deposit, defeasance and discharge had not occurred.

Defeasance of Certain Covenants. The indenture provides that, upon compliance with certain conditions, we may be released from our obligation to comply with certain covenants set forth in the indenture and any supplemental indenture, and any failure to comply with those covenants will not constitute a default or an event of default with respect to the debt securities of the applicable series, or covenant defeasance. If we exercise our covenant defeasance option with respect to a series of debt securities, payment of such debt securities may not be accelerated because of an event of default related to certain events of bankruptcy, insolvency or reorganization of our significant subsidiaries.

The conditions include:

Governing Law

The indenture and the debt securities will be governed by, and construed in accordance with, the internal laws of the State of New York.

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Description of Purchase Contracts

We may issue purchase contracts, including contracts obligating holders to purchase from us, and obligating us to sell to the holders, a specified number of common shares or other securities at a future date or dates. The price per security of the securities and the number of securities may be fixed at the time the purchase contracts are issued or may be determined by reference to a specific formula set forth in the purchase contracts. The purchase contracts also may require us to make periodic payments to the holders of the purchase contracts, or vice versa, and those payments may be unsecured or refunded on some basis. The purchase contracts may require holders to secure their obligations thereunder in a specified manner and may provide for the prepayment of all or part of the consideration payable by holders in connection with the purchase of the underlying security or other property pursuant to the purchase contracts.

The securities related to the purchase contracts may be pledged to a collateral agent for our benefit pursuant to a pledge agreement to secure the obligations of holders of purchase contracts to purchase the underlying security or property under the related purchase contracts. The rights of holders of purchase contracts to the related pledged securities will be subject to our security interest therein created by the pledge agreement. No holder of purchase contracts will be permitted to withdraw the pledged securities related to such purchase contracts from the pledge arrangement.

The prospectus supplement relating to any particular issuance of purchase contracts will describe the terms of the purchase contracts. The description in the prospectus supplement will not necessarily be complete, and reference will be made to the purchase contracts, and, if applicable, collateral or depositary arrangements, relating to the purchase contracts, which will be filed with the SEC each time we issue purchase contracts. U.S. federal income tax considerations applicable to the purchase contracts will also be discussed in the prospectus supplement.

Description of Units

We may issue units comprising one or more securities described in this prospectus in any combination. The following description sets forth certain general terms and provisions of the units that we may offer pursuant to this prospectus. The particular terms of the units and the extent, if any, to which the general terms and provisions may apply to the units so offered will be described in the applicable prospectus supplement.

Each unit will be issued so that the holder of the unit also is the holder of each security included in the unit. Thus, the unit will have the rights and obligations of a holder of each included security. Units will be issued pursuant to the terms of a unit agreement, which may provide that the securities included in the unit may not be held or transferred separately at any time or at any time before a specified date. A copy of the forms of the unit agreement and the unit certificate relating to any particular issue of units will be filed with the SEC each time we issue units, and you should read those documents for provisions that may be important to you. For more information on how you can obtain copies of the forms of the unit agreement and the related unit certificate, see “Where You Can Find More Information.”

The prospectus supplement relating to any particular issuance of units will describe the terms of those units, including, to the extent applicable, the following:

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Plan of Distribution

We may sell the offered securities in and outside the United States:

The prospectus supplement will include the following information:

Sale through Underwriters or Dealers

If underwriters are used in the sale, the underwriters will acquire the securities for their own account. The underwriters may resell the securities from time to time in one or more transactions, including negotiated transactions, at a fixed public offering price or at varying prices determined at the time of sale. Underwriters may offer securities to the public either through underwriting syndicates represented by one or more managing underwriters or directly by one or more firms acting as underwriters. Unless we inform you otherwise in the prospectus supplement, the obligations of the underwriters to purchase the securities will be subject to certain conditions, and the underwriters will be obligated to purchase all the offered securities if they purchase any of them. The underwriters may change, from time to time, any initial public offering price and any discounts or concessions allowed or reallowed or paid to dealers.

If we offer securities in a subscription rights offering to our existing security holders, we may enter into a standby underwriting agreement with dealers, acting as standby underwriters. We may pay the standby underwriters a commitment fee for the securities they commit to purchase on a standby basis. If we do not enter into a standby underwriting agreement, we may retain a dealer-manager to manage a subscription rights offering for us.

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During and after an offering through underwriters, the underwriters may purchase and sell the securities in the open market. These transactions may include overallotment and stabilizing transactions and purchases to cover syndicate short positions created in connection with the offering. The underwriters may also impose a penalty bid, which means that selling concessions allowed to syndicate members or other broker-dealers for the offered securities sold for their account may be reclaimed by the syndicate if the offered securities are repurchased by the syndicate in stabilizing or covering transactions. These activities may stabilize, maintain or otherwise affect the market price of the offered securities, which may be higher than the price that might otherwise prevail in the open market. If commenced, the underwriters may discontinue these activities at any time.

Some or all of the securities that we offer though this prospectus may be new issues of securities with no established trading market. Any underwriters to whom we sell our securities for public offering and sale may make a market in those securities, but they will not be obligated to do so and they may discontinue any market making at any time without notice. Accordingly, we cannot assure you of the liquidity of, or continued trading markets for, any securities that we offer.

If dealers are used in the sale of securities, we will sell the securities to them as principals. They may then resell those securities to the public at varying prices determined by the dealers at the time of resale. We will include in the prospectus supplement the names of the dealers and the terms of the transaction.

Direct Sales and Sales through Agents

We may sell the securities directly. In this case, no underwriters or agents would be involved. We may also sell the securities through agents designated from time to time at fixed prices or at varying prices determined at the time of sale. In the prospectus supplement, we will name any agent involved in the offer or sale of the offered securities, and we will describe any commissions payable to the agent. Unless we inform you otherwise in the prospectus supplement, any agent will agree to use its reasonable best efforts to solicit purchases for the period of its appointment.

We may sell the securities directly to institutional investors or others who may be deemed to be underwriters within the meaning of the Securities Act with respect to any sale of those securities. We will describe the terms of any sales of these securities in the prospectus supplement.

Remarketing Arrangements

Offered securities may also be offered and sold, if so indicated in the applicable prospectus supplement, in connection with a remarketing upon their purchase, in accordance with a redemption or repayment pursuant to their terms, or otherwise, by one or more remarketing firms, acting as principals for their own accounts or as agents for us. Any remarketing firm will be identified and the terms of its agreements, if any, with us and its compensation will be described in the applicable prospectus supplement.

Delayed Delivery Contracts

If we so indicate in the prospectus supplement, we may authorize agents, underwriters or dealers to solicit offers from certain types of institutions to purchase securities from us at the public offering price under delayed delivery contracts. These contracts would provide for payment and delivery on a specified date in the future. The contracts would be subject only to those conditions described in the prospectus supplement. The prospectus supplement will describe the commission payable for solicitation of those contracts.

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General Information

We may have agreements with the agents, dealers, underwriters and remarketing firms to indemnify them against certain civil liabilities, including liabilities under the Securities Act, or to contribute with respect to payments that the agents, dealers, underwriters or remarketing firms may be required to make. Agents, dealers, underwriters and remarketing firms may be customers of, engage in transactions with or perform services for us in the ordinary course of their businesses.

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Legal Matters

Jones Day will pass upon the validity of the securities being offered hereby. Any underwriters will be advised about other issues to any offering by their own legal counsel.

Experts

The consolidated financial statements as of December 31, 2021 and 2020 and for each of the three years in the period ended December 31, 2021 and management’s assessment of the effectiveness of internal control over financial reporting as of December 31, 2021 incorporated by reference in this Prospectus have been so incorporated in reliance on the reports of BDO USA, LLP, an independent registered public accounting firm, incorporated herein by reference, given on the authority of said firm as experts in auditing and accounting.

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PART II

INFORMATION NOT REQUIRED IN PROSPECTUS

The following table sets forth the estimated expenses in connection with the issuance and distribution of an assumed amount of $150,000,000 of securities registered under this registration statement, other than any underwriting discounts and commissions. All of the expenses will be borne by us except as otherwise indicated.

Pursuant to the provisions of the General Corporation Law of the State of Delaware (“DGCL”), CECO has adopted provisions in its certificate of incorporation and bylaws that require CECO to indemnify its officers and directors to the fullest extent permitted by law, and eliminate the personal liability of its directors to CECO or CECO’s stockholders for monetary damages for breach of their duty of due care except (a) for any breach of the directors’ duty of loyalty to the corporation or its stockholders, (b) for acts or omissions not in good faith or which involve intentional misconduct or a knowing violation of law, (c) for acts relating to unlawful payment of a dividend or an unlawful stock purchase or redemption or (d) for any transaction from which the director derived an improper personal benefit. These provisions do not eliminate a director’s duty of care. Moreover, the provisions do not apply to claims against a director for violation of certain laws, including federal securities laws.

CECO’s certificate of incorporation and bylaws provide for mandatory indemnification of officers and directors of the corporation, including a director or officer of the corporation who is serving at the request of the corporation as a director, officer, employee or agent of another corporation, partnership, joint venture, trust or other enterprise, to the fullest extent permitted under the DGCL. CECO may also, at its discretion, provide the same benefits of indemnification to any employee or agent of the corporation. Also, CECO is authorized to purchase insurance on behalf of an individual for liabilities incurred whether or not CECO would have the power or obligation to indemnify him or her under our bylaws.

II-1

The following documents are exhibits to the registration statement:

The undersigned registrant hereby undertakes:

II-2

Provided, however, that:

II-3

The undersigned registrant undertakes that in a primary offering of securities of the undersigned registrant pursuant to this registration statement, regardless of the underwriting method used to sell the securities to the purchaser, if the securities are offered or sold to such purchaser by means of any of the following communications, the undersigned registrant will be a seller to the purchaser and will be considered to offer or sell such securities to such purchaser:

II-4

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Dallas, State of Texas, on April 29, 2022.

KNOW ALL MEN BY THESE PRESENTS, that each individual whose signature appears below constitutes and appoints Todd Gleason, Ramesh Nuggihalli, Matthew Eckl, Paul Gohr and Alyson Gregory Richter, and each of them, his or her true and lawful attorneys-in-fact and agents with full power of substitution, for him or her and in his or her name, place and stead, in any and all capacities, to sign any and all amendments (including post-effective amendments) to this registration statement, and to file the same, with all exhibits thereto, and all documents in connection therewith, with the U.S. Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents, or his, her or their substitutes, may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, this registration statement on Form S-3 has been signed below by the following persons in the capacities indicated as of the dates indicated below:

II-5

II-6

Exhibit 5.1

NORTH POINT • 901 LAKESIDE AVENUE • CLEVELAND, OHIO 44114.1190

TELEPHONE: +1.216.586.3939 • FACSIMILE: +1.216.579.0212

May 2, 2022

CECO Environmental Corp.

14651 North Dallas Parkway, Suite 500

Dallas, Texas 75254

Ladies and Gentlemen:

We have acted as counsel for CECO Environmental Corp., a Delaware corporation (the “Company”), in connection with the authorization of the possible issuance and sale from time to time, on a delayed basis, by the Company of up to $150,000,000 in initial aggregate offering price of: (i) shares of common stock, par value $0.01 per share, of the Company (the “Common Stock”); (ii) shares of preferred stock, par value $0.01 per share, of the Company (the “Preferred Stock”), in one or more series, certain of which may be convertible into or exchangeable for shares of Common Stock; (iii) debt securities of the Company (the “Debt Securities”), in one or more series, certain of which may be convertible into or exchangeable for shares of Common Stock; (iv) depositary shares representing fractional interests in shares of Preferred Stock (the “Depositary Shares”); (v) warrants to purchase shares of Common Stock, shares of Preferred Stock, Depositary Shares or Debt Securities or any combination thereof (the “Warrants”); (vi) subscription rights to purchase shares of Common Stock, shares of Preferred Stock, Depositary Shares or Debt Securities or any combination thereof (the “Subscription Rights”); (vii) purchase contracts (the “Purchase Contracts”) to purchase securities at a future date or dates; and (viii) units consisting of one or more of the securities described in clauses (i) through (vii) above (the “Units”), in each case as contemplated by the Company’s Registration Statement on Form S-3 to which this opinion is filed as an exhibit (as the same may be amended from time to time, the “Registration Statement”). The Common Stock, the Preferred Stock, the Debt Securities, the Depositary Shares, the Warrants, the Subscription Rights, the Purchase Contracts and the Units are collectively referred to herein as the “Securities.” The Securities may be offered and sold from time to time pursuant to Rule 415 under the Securities Act of 1933 (the “Securities Act”).

In connection with the opinions expressed herein, we have examined such documents, records and matters of law as we have deemed relevant or necessary for purposes of such opinions. Based on the foregoing, and subject to the further limitations, qualifications and assumptions set forth herein, we are of the opinion that:

AMSTERDAM • ATLANTA • BEIJING • BOSTON • BRISBANE • BRUSSELS • CHICAGO • CLEVELAND • COLUMBUS • DALLAS • DETROIT

DUBAI • DÜSSELDORF • FRANKFURT • HONG KONG • HOUSTON • IRVINE • LONDON • LOS ANGELES • MADRID • MELBOURNE

MEXICO CITY • MIAMI • MILAN • MINNEAPOLIS • MUNICH • NEW YORK • PARIS • PERTH • PITTSBURGH • SAN DIEGO • SAN FRANCISCO

SĂO PAULO • SAUDI ARABIA • SHANGHAI • SILICON VALLEY • SINGAPORE • SYDNEY • TAIPEI • TOKYO • WASHINGTON

CECO Environmental Corp. May 2, 2022 Page 2

In rendering the foregoing opinions, we have assumed that: (i) the Registration Statement, and any amendments thereto, will have become effective (and will remain effective at the time of issuance of any Securities thereunder); (ii) a prospectus supplement describing each class and/or series of Securities offered pursuant to the Registration Statement, to the extent required by applicable law and relevant rules and regulations of the Securities and Exchange Commission (the “Commission”), will be timely filed with the Commission; (iii) the definitive terms of each class and/or series of Securities will have been established in accordance with the authorizing resolutions adopted by the Company’s Board of Directors (or an authorized committee thereof), the Company’s Certificate of Incorporation (the “Certificate of Incorporation”) and applicable law; (iv) the Company will issue and deliver the Securities in the manner contemplated by the Registration Statement and any Securities that consist of shares of capital stock will have been authorized and reserved for issuance, in each case within the limits of the then remaining authorized but unissued and unreserved amounts of such capital stock; (v) the resolutions authorizing the Company to issue, offer and sell the Securities will have been adopted by the Company’s Board of Directors (or an authorized committee thereof) and will be in full force and effect at all times at which the Securities are offered or sold by the Company; (vi) all Securities will be issued in compliance with applicable federal and state securities laws and (vii) the Indenture (as defined below) and any Deposit Agreement, Warrant Agreement, Subscription Rights Agreement, Purchase Contract Agreement (each as defined below) or unit agreement will be governed by and construed in accordance with the laws of the State of New York and will constitute a valid and binding obligation of each party thereto other than the Company.

With respect to any Securities consisting of Preferred Stock, we have further assumed that the Company will issue and deliver the shares of the Preferred Stock being issued and delivered after the filing with the Secretary of State of the State of Delaware of a certificate of designation to the Certificate of Incorporation, in a form approved by us, establishing the designations, preferences and rights of the class or series of the Preferred Stock being issued and delivered.

With respect to any Securities consisting of any series of Debt Securities, we have further assumed that: (i) an indenture with respect to such Debt Securities will have been authorized, executed and delivered by the Company and the applicable trustee in a form approved by us (the “Indenture”), and the Indenture will have been qualified

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May 2, 2022

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under the Trust Indenture Act of 1939; (ii) such Debt Securities will have been issued pursuant to the Indenture; (iii) all terms of such Debt Securities not provided for in the applicable Indenture will have been established in accordance with the provisions of the Indenture and reflected in appropriate documentation approved by us and, if applicable, executed and delivered by the Company and the trustee; and (iv) such Debt Securities will be executed, authenticated, issued and delivered in accordance with the provisions of the Indenture.

With respect to any Securities consisting of Depositary Shares, we have further assumed that the Depositary Shares will be: (i) issued and delivered after authorization, execution and delivery of the deposit agreement, approved by us, relating to the Depositary Shares to be entered into between the Company and an entity (the “Depositary”) selected by the Company to act as depositary (the “Deposit Agreement”); and (ii) issued after the Company deposits with the Depositary shares of the Preferred Stock to be represented by such Depositary Shares that are authorized, validly issued, fully paid and nonassessable as contemplated by the Registration Statement and the Deposit Agreement.

With respect to any Securities consisting of Warrants, we have further assumed that: (i) the warrant agreement, approved by us, relating to the Warrants (the “Warrant Agreement”) to be entered into between the Company and an entity selected by the Company to act as the warrant agent (the “Warrant Agent”) will have been authorized, executed and delivered by the Company and the Warrant Agent; and (ii) the Warrants will be authorized, executed and delivered by the Company and the Warrant Agent in accordance with the provisions of the Warrant Agreement.

With respect to any Securities consisting of Subscription Rights, we have further assumed that: (i) the subscription rights agreement, approved by us, relating to the Subscription Rights (the “Subscription Rights Agreement”) to be entered into between the Company and an entity selected by the Company to act as the subscription rights agent (the “Subscription Rights Agent”) will have been authorized, executed and delivered by the Company and the Subscription Rights Agent; and (ii) the Subscription Rights will be authorized, executed and delivered by the Company and the Subscription Rights Agent in accordance with the provisions of the Subscription Rights Agreement.

With respect to any Securities consisting of Purchase Contracts, we have further assumed that: (i) the purchase contract agreement, approved by us, relating to the Purchase Contracts (the “Purchase Contract Agreement”) to be entered into between the Company and an entity selected by the Company to act as the purchase contract agent (the “Purchase Contract Agent”) will have been authorized, executed and delivered by the Company and the Purchase Contract Agent; and (ii) the Purchase Contracts will be authorized, executed and delivered by the Company and the Purchase Contract Agent in accordance with the provisions of the Purchase Contract Agreement.

With respect to any Securities consisting of Units, we have further assumed that each component of such Unit will be authorized, validly issued, fully paid and nonassessable (to the extent applicable) and will constitute a valid and binding obligation of the Company or any third party (to the extent applicable) as contemplated by the Registration Statement and the applicable unit agreement, if any.

The opinions expressed herein are limited by bankruptcy, insolvency, reorganization, fraudulent transfer and fraudulent conveyance, voidable preference, moratorium or other similar laws and related regulations and judicial doctrines from time to time in effect relating to or affecting creditors’ rights generally, and by general equitable principles and public policy considerations, whether such principles and considerations are considered in a proceeding at law or at equity.

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May 2, 2022

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As to facts material to the opinions and assumptions expressed herein, we have relied upon oral or written statements and representations of officers and other representatives of the Company and others. The opinions expressed herein are limited to the General Corporation Law of the State of Delaware and the laws of the State of New York, in each case as currently in effect, and we express no opinion as to the effect of the laws of any other jurisdiction.

We hereby consent to the filing of this opinion as Exhibit 5.1 to the Registration Statement and to the reference to Jones Day under the caption “Legal Matters” in the prospectus constituting a part of the Registration Statement. In giving such consent, we do not thereby admit that we are included in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission promulgated thereunder.

Exhibit 23.1

Consent of Independent Registered Public Accounting Firm

CECO Environmental Corp. and Subsidiaries

Dallas, Texas

We hereby consent to the incorporation by reference in the Prospectus constituting a part of this Registration Statement of our reports dated March 14, 2022, relating to the consolidated financial statements and the effectiveness of CECO Environmental Corp. and Subsidiaries’ internal control over financial reporting appearing in the Company’s Annual Report on Form 10-K for the year ended December 31, 2021.

We also consent to the reference to us under the caption “Experts” in the Prospectus.

/s/ BDO USA, LLP

Cincinnati, Ohio

May 2, 2022

Exhibit 107

Calculation of Filing Fee Tables

S-3

(Form Type)

CECO Environmental Corp.

(Exact Name of Registrant as Specified in its Charter)

Table 1: Newly Registered and Carry Forward Securities

Table 2: Fee Offset Claims and Sources