As filed with the Securities and Exchange Commission on June 1, 2026

Registration No. 333-

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549

FORM S-8

REGISTRATION STATEMENT
UNDER THE SECURITIES ACT OF 1933

CECO ENVIRONMENTAL CORP.
(Exact name of registrant as specified in its charter)

CECO Environmental Corp. 2026 Equity and Incentive Compensation Plan

Thermon Group Holdings, Inc. 2020 Long-Term Incentive Plan

(Full titles of the plans)

Alyson Gregory
General Counsel & Corporate Secretary
CECO Environmental Corp.
5080 Spectrum Drive, Suite 800E
Addison, Texas 75001

(214) 357-6181
(Name, address and telephone of agent for service)

Copies to:

Gina Hancock

Gibson, Dunn & Crutcher LLP

2001 Ross Avenue, Suite 2100

Dallas, Texas 75201

(214) 698-3100

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a 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. ☐

Explanatory Note

On June 1, 2026, 2026, CECO Environmental Corp. (“CECO” or the “Registrant”) completed its acquisition of Thermon Group Holdings, Inc., a Delaware corporation (“Thermon”). In accordance with the Agreement and Plan of Merger, dated as of February 23, 2026 (the “Merger Agreement”), by and among CECO, Thermon, Longhorn Merger Sub LLC and Longhorn Merger Sub, Inc., CECO assumed certain Thermon equity awards that were outstanding as of immediately prior to the effective time of the merger under the Thermon Group Holdings, Inc. 2020 Long-Term Incentive Plan (as amended, the “Thermon Equity Plan,” and such awards, the “Assumed Awards”). The Assumed Awards were converted into awards of restricted stock units of CECO that represent a right to receive shares of common stock, par value $0.01 per share, of CECO (the “Common Stock”) but remain subject to the same terms and conditions (including with respect to time-based vesting but excluding performance-based vesting conditions) that were applicable to the corresponding awards under the Thermon Equity Plan, as adjusted to give effect to the exchange ratio under the Merger Agreement.

In addition, on May 27, 2026, the Registrant’s stockholders approved the CECO Environmental Corp. 2026 Equity and Incentive Compensation Plan (the “2026 Plan”).

This Registration Statement on Form S-8 (this “Registration Statement”) is being filed by CECO for the purpose of registering (i) 420,370 shares of Common Stock that may be offered and sold under the Thermon Equity Plan, (ii) 3,549,986 shares of Common Stock that may be offered and sold under the 2026 Plan and (iii) 887,514 shares of Common Stock that may become available for delivery under the 2026 Plan pursuant to the share recycling and share counting provisions thereof.

PART I
INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

The documents containing the information specified in Part I of Form S-8 will be sent or given to participants as specified by Rule 428(b)(1) of the Securities Act of 1933, as amended (the “Securities Act”). In accordance with the instructions to Part I of Form S-8, such documents are not being filed with the Securities and Exchange Commission (the “SEC”) either as part of this Registration Statement or as prospectuses or prospectus supplements pursuant to Rule 424 of the Securities Act. Such documents and the documents incorporated by reference in this Registration Statement pursuant to Item 3 of Part II of Form S-8, taken together, constitute a prospectus that meets the requirements of Section 10(a) of the Securities Act.

PART II
Information Required in the Registration Statement

Item 3. Incorporation of Documents by Reference

The following documents, which have previously been filed by the Registrant with the SEC pursuant to the Securities Act and pursuant to the Securities Exchange Act of 1934, as amended (the “Exchange Act”), are incorporated by reference into this Registration Statement and shall be deemed to be a part hereof:

In addition, all documents subsequently filed by the Registrant with the SEC pursuant to Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act prior to the filing of a post-effective amendment to this Registration Statement which indicates that all securities offered hereby have been sold or which deregisters all such securities then remaining unsold, shall be deemed to be incorporated by reference in this Registration Statement and to be a part hereof from the date of filing of such documents. Notwithstanding the foregoing, unless specifically stated to the contrary, none of the information that the Registrant discloses under Items 2.02 or 7.01 of any Current Report on Form 8-K that it may from time to time furnish to the SEC will be incorporated by reference into, or otherwise included in, this Registration Statement.

Any statement, including financial statements, contained in a document incorporated or deemed to be incorporated by reference herein shall be deemed to be modified or superseded for purposes of this Registration Statement to the extent that a statement contained herein or therein or in any other subsequently filed document which 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 Registration Statement.

Item 4. Description of Securities

Not applicable.

Item 5. Interests of Named Experts and Counsel

Not applicable.

Item 6. Indemnification of Directors and Officers

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 and officers 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) in the case of directors only, for acts relating to unlawful payment of a dividend or an unlawful stock purchase or redemption, (d) for any transaction from which the director or officer derived an improper personal benefit, or (e) in the case of officers only, for any action by or in the right of CECO. 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.

Item 7. Exemption from Registration Claimed

Not applicable.

Item 8. Exhibits

*Filed herewith.

Item 9. Undertakings

provided, however, that paragraphs (1)(i) and (1)(ii) do not apply if the information required to be included in a post-effective amendment by those paragraphs is contained in reports filed with or furnished to the Commission by the Registrant pursuant to Section 13 or Section 15(d) of the Exchange Act that are incorporated by reference herein.

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-8 and has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Addison, State of Texas on June 1, 2026.

POWER OF ATTORNEY

KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears below hereby constitutes and appoints each of Todd Gleason and Alyson Richter and each of them acting individually, as his or her true and lawful attorneys-in-fact and agents, each with full power of substitution and resubstitution in each of them singly, for such person and in such person’s name, place and stead, and 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 other documents in connection therewith, with the SEC, granting to the attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in or about the premises, as fully to all intents and purposes as such person might, or could do in person, hereby ratifying and confirming all that the attorneys-in-fact and agents or any of each of them or their substitutes may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act, this Registration Statement has been signed by the following persons in the capacities and on the dates indicated.

ATTACHMENTS / EXHIBITS

EXHIBIT 5.1

EXHIBIT 23.1

EXHIBIT 23.2

EXHIBIT 23.3

EXHIBIT 99.2

EX-FILING FEES

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