NOTWITHSTANDING ANYTHING HEREIN TO THE CONTRARY, (I) THE OBLIGATIONS EVIDENCED
BY THIS THIRD AMENDED AND RESTATED REPLACEMENT PROMISSORY NOTE ARE SUBORDINATED
TO THE PRIOR PAYMENT IN FULL OF THE SENIOR OBLIGATIONS (AS DEFINED IN THE
SUBORDINATION AGREEMENT HEREINAFTER REFERRED TO) PURSUANT TO, AND TO THE EXTENT
PROVIDED IN THE SUBORDINATION AGREEMENT, DATED AS OF DECEMBER 29, 2005 (AS
AMENDED, RESTATED, SUPPLEMENTED OR MODIFIED FROM TIME TO TIME, THE
“SUBORDINATION AGREEMENT”) IN FAVOR OF FIFTH THIRD BANK (TOGETHER WITH ITS
SUCCESSORS AND ASSIGNS, AND THE OTHER HOLDERS, IF ANY, OF THE SENIOR OBLIGATIONS
IDENTIFIED THEREIN, THE “SENIOR LENDER”) AND (II) THE RIGHTS OF THE HOLDER OF
THIS NOTE HEREUNDER ARE SUBJECT TO THE LIMITATIONS AND PROVISIONS OF THE
SUBORDINATION AGREEMENT. IN THE EVENT OF ANY CONFLICT BETWEEN THE TERMS OF THE
SUBORDINATION AGREEMENT AND THE TERMS OF THIS THIRD AMENDED AND RESTATED
REPLACEMENT PROMISSORY NOTE, THE TERMS OF THE SUBORDINATION AGREEMENT SHALL
GOVERN.

CECO Environmental Corp.

FOURTH AMENDED AND RESTATED REPLACEMENT PROMISSORY NOTE

$1,200,000

March 26, 2007

     WHEREAS, Can-Med Technology, Inc. d/b/a Green Diamond Oil Corp., an Ontario
corporation ("Green Diamond") has prior to this date advanced sums to CECO
Environmental Corp. (the "Company") as evidenced by a Third Amended and Restated
Replacement Promissory Note dated December 28, 2006 (the "Prior Note"), which
Prior Note shall be cancelled and replaced by this Fourth Amended and Restated
Replacement Promissory Note (the "Note").

     WHEREAS, Green Diamond has agreed to amend and restate the Prior Note and
replace the Prior Note with this Note to extend the maturity date and increase
the interest rate under the Prior Note.

     FOR VALUE RECEIVED, the undersigned, CECO Environmental Corp. (the
“Company”), a Delaware corporation, hereby promises to pay to the order of Green
Diamond Oil Corp. or registered assigns (“Holder”), the principal sum of ONE
MILLION TWO HUNDRED THOUSAND AND NO/100 ($1,200,000.00) on the Maturity Date, as
defined in Section 1 below. This Note is subordinate to certain bank financing
of the Company further described herein and to a series of promissory notes in
the original principal amount of $5,000,000 originally issued on December 2,
1999 and subsequently amended and restated (the "December 1999 Notes"). The
principal amount of the December 1999 Notes has been increased in connection
with an amendment and restatement.

112527v1

--------------------------------------------------------------------------------

     1. Maturity. This Note shall be due and payable upon the earlier to occur
of the following events (the “Maturity Date”): (i) January 31, 2010 or (ii) the
closing (any such closing referred to as the “Closing”) of a Sale Transaction.
For purposes of this Note, a Sale Transaction shall mean (i) a merger,
consolidation, corporate reorganization, or sale of shares of stock of the
Company as a result of which there is a change in control and/or the
shareholders of the Company on the date hereof (“Current Shareholders”) own 50%
or less of the outstanding shares of the Company on a fully-diluted basis
immediately after the transaction and, including as outstanding for purposes of
such calculation, any warrants, options or other instruments convertible or
exchangeable into equity securities of the Company issued to persons other than
the Current Shareholders in connection with the transaction or (ii) the sale of
(A) fifty percent or more of the assets of the Company or (B) any subsidiary,
division or line of business of the Company for total consideration in excess of
$5 million.

     2. Interest. Interest shall accrue on the unpaid principal balance hereof
and on any interest payment that is not made when due at the simple compounded
rate of twelve percent (12%) per annum. Accrued interest shall be due and
payable on March 31 and September 30 of each year and on the Maturity Date. It
shall not be a default hereunder and interest will not accrue on any portion of
such interest payments deferred pursuant to the Subordination Agreement
("Deferred Interest") so long as the Deferred Interest is paid at the time and
in the manner allowed by the Subordination Agreement (as defined herein). In the
Event of Default (as defined herein), interest shall accrue on all unpaid
amounts due hereunder including without limitation, interest, at the rate of
fifteen percent (15%) per annum. If a judgment is entered against the Company on
this Note, the amount of the judgment so entered shall bear interest at the
highest rate authorized by law as of the date of the entry of the judgment.

     3. Payments. Payments of both principal and interest shall be made at the
Company's office in Toronto, Ontario, or such other place as the Holder hereof
shall designate to the Company in writing, in lawful money of the United States
of America. So long as no Event of Default has occurred in this Note, all
payments hereunder shall first be applied to interest, then to principal. Upon
the occurrence of an Event of Default in this Note, all payments hereunder shall
first be applied to costs pursuant to Section 10.5, then to interest and the
remainder to principal.

     4. Registered Owner. Prior to due presentation for registration of
transfer, the Company may treat the person in whose name this Note is registered
as the owner and holder of such Note for the purpose of receiving payment of
principal of, and interest on, this Note and for all other purposes.

5.      Prepayment.     5.1 Optional Prepayment. The Company, at its option and
without any  

premium, may prepay in whole or in part the principal amount of this Note at any
time. The Company shall, at the time of any such prepayment, pay to the holder
of this Note all interest accrued and unpaid to the Prepayment Date (defined
below). Notwithstanding the foregoing, once a notice of the Closing of a Sale
Transaction pursuant to Section 10.4

112527v1

2

--------------------------------------------------------------------------------

has been sent to the Holder, the Company may not prepay this Note prior to the
Closing of a Sale Transaction, or until the Sale Transaction has been formally
abandoned.

     5.2 Notice of Prepayment. At least five (5) but not more than fifteen (15)
days prior to the date fixed for any prepayment, written notice shall be given
to the holder of this Note of the election of the Company to prepay all or a
specified portion of the principal amount of the Note (the “Prepayment
Notice.”). The Prepayment Notice shall specify the date upon (“Prepayment Date”)
and the place at which, payment may be obtained and shall call upon the Holder
to surrender this Note to the Company in the manner and at the place designated.
On the Prepayment Date, the Holder shall surrender this Note to the Company in
the manner and at the place designated in the Prepayment Notice, and thereupon
prepayment shall be made to Holder and this Note shall be cancelled. In the
event that less than all the principal amount of this Note is prepaid, upon
surrender of this Note to the Company, the Company shall execute and deliver to
Holder a new Note or Notes in principal amount equal to the unpaid principal
amount of this Note.

     5.3 Cessation of Rights. From and after the Prepayment Date, unless there
has been a default under the Prepayment Notice, all interest on the redeemed
principal amount shall cease to accrue and all rights of Holder as a Holder of
this Note shall cease with respect to the principal amount prepaid and, with
respect to such amount, this Note thereafter shall not be deemed to be
outstanding for any purpose whatsoever. By acceptance of this Note, Holder
agrees to execute and deliver such documents as may be reasonably requested from
time to time by the Company in order to implement the foregoing provisions of
this Section.

     6. Subordination. The indebtedness evidenced by this Note shall at all
times be wholly subordinate and junior in right of payment to all obligations of
the Company under or in connection with the Credit Agreement dated December 29,
2005 (“Superior Debt”) among the Company, CECO Group Inc., CECO Filters, Inc.,
New Bush Co., Inc., The Kirk & Blum Manufacturing Company, kbd/Technic, Inc.,
CECOAire, Inc., CECO Abatement Systems, Inc. and Fifth Third Bank, upon the
terms and conditions contained in the Subordination Agreement, dated as of
December 29, 2005 (as amended, restated, supplemented or modified from time to
time, the “Subordination Agreement”) in favor of Fifth Third Bank (together with
its successors and assigns, and the other holders, if any, of the Senior
Obligations identified therein). This Note also is subordinate to the December
1999 Notes, and no payments of principal or interest shall be made under this
Note, if an Event of Default (as defined in the December 1999 Notes) is existing
under any of the December 1999 Notes.

     7. Covenants of the Company. The Company covenants and agrees that it shall
not, without the prior written approval of the Holder:

7.1 Obtain or incur any indebtedness or other monetary obligations that are
senior to or on parity with this Note, other than the Superior Debt and the
December 1999 Notes.

112527v1

3

--------------------------------------------------------------------------------

7.2 Allow, suffer or cause to exist any lien, claim, security interest or
encumbrance on the Company’s property or assets, other than with respect to the
Superior Debt and purchase money indebtedness incurred in the ordinary course of
business.

7.3 Enter into any arrangement or agreement involving the merger or
consolidation of the Company.

7.4 Use the proceeds from this Note other than in the ordinary course of its
business for general corporate purposes including lending monies to any of its
subsidiaries. The Company also covenants and agrees that it shall operate its
business in the ordinary course.

8.      Events of Default.     8.1 Occurrences of Events of Default. Each of the
following events shall constitute an “Event of Default” for purposes of this
Note:  

(a)      if the Company fails to pay any amount payable, under this Note when
due;   (b)      if the Company breaches any of its representations, warranties
or covenants set forth in this Note;   (c)      the commencement of an
involuntary case against the Company or its subsidiary or any of its
subsidiaries under any applicable bankruptcy, insolvency or other similar law
now or hereafter in effect, or the appointing of a receiver, liquidator,
assignee, custodian, trustee or similar official of the Company or for any
substantial part of the Company or one of its subsidiary’s property, or ordering
the winding-up or liquidation of the Company or one of its subsidiary’s affairs;
  (d)      if the Company or any of its subsidiaries shall commence a voluntary
case under any applicable bankruptcy, insolvency or other similar law now or
hereafter in effect, or shall consent to the entry of an order for relief in an
involuntary case under any such law, or shall consent to the appointment of or
taking possession by a receiver, liquidator, assignee, trustee, custodian or
similar official of the Company or its subsidiary or for any substantial part of
the Company or one of its subsidiary’s property, or shall make any general
assignment for the benefit of creditors, or shall take any corporate action in
furtherance of any of the foregoing; or  

112527v1

4

--------------------------------------------------------------------------------

(e) if the Company’s business shall fail, as determined in good faith by the
Holder and evidenced by the Company’s inability to pay its ongoing debts as such
debts become due.

8.2 Acceleration Upon Event of Default. If any Event of Default shall have
occurred and be continuing, for any reason whatsoever (and whether such
occurrence shall be voluntary or involuntary or come about or be effected by
operation of law or otherwise), the unpaid principal amount of, and the accrued
interest on, this Note shall automatically become immediately due and payable,
without presentment, demand, protest or other requirements of any kind, all of
which are hereby expressly waived by the Company.

     9. Investment Representations of the Holder. With respect to the purchase
of this Note, the Holder hereby represents and warrants to the Company as
follows:

     9.1 Experience. The Holder has substantial experience in evaluating and
investing in private transactions of securities in companies similar to the
Company so that it is capable of evaluating the merits and risks of its
investment in the Company and has the capacity to protect its own interests.

     9.2 Status. The Holder is an “accredited investor” within the meaning of
Regulation D, Section 501(a), promulgated by the Securities and Exchange
Commission, and is acquiring this Note for investment for its own account, not
as a nominee or agent, and not with a view to, or for resale or transfer.

     9.3 Access to Data. The Holder has had an opportunity to discuss the
Company’s business, management and financial affairs with the Company’s
management and has also had an opportunity to ask questions of the Company’s
officers, which questions were answered to its satisfaction.

10.      Miscellaneous.     10.1 Invalidity of Any Provision. If any provision
or part of any provision of  

this Note shall for any reason be held invalid, illegal or unenforceable in any
respect, such invalidity, illegality or unenforceability shall not affect any
other provisions of this Note and this Note shall be construed as if such
invalid, illegal or unenforceable provisions or part hereof had never been
contained herein, but only to the extent of its invalidity, illegality or
unenforceability.

     10.2 Governing Law. The Note shall be governed in all respects by the laws
of the State of Delaware, excluding its conflict of laws.

     10.3 Notices. Any notice or other communication required or permitted
hereunder shall be in writing and shall be deemed to have been duly given (i) on
the date of delivery if delivered personally, (ii) one (1) business day after
transmission by facsimile

112527v1

5

--------------------------------------------------------------------------------

transmission with a written confirmation copy sent by first class mail, or (iii)
five (5) days after mailing if mailed by first class mail, to the following
addresses:

If to the Holder:    Green Diamond Corp.      505 University Avenue, Suite 1400 
    Toronto, Ontario M5G 1X3      Canada      Attention: Phillip DeZwirek    If
to the Company:    CECO Environmental Corp.      3120 Forrer Street     
Cincinnati, Ohio 45209      Attention: Dennis W. Blazer 

     10.4 Notice of a Sale Transaction. The Company shall give the Holder of
this Note notice of the Closing of a Sale Transaction at least thirty (30) days
prior to such Closing.

     10.5 Collection. If the indebtedness represented by this Note or any part
thereof is collected at law or in equity or in bankruptcy, receivership or other
judicial proceedings or if this Note is placed in the hands of attorneys for
collection after the occurrence of an Event of Default, the Company agrees to
pay, in addition to the outstanding principal and accrued interest payable
hereon, reasonable attorneys’ fees and costs incurred by the Holder, or on
behalf of the Holder by a representative of the Holder.

     10.6 Successors and Assigns. The rights and obligations of the Company and
the Holder shall be binding upon and benefit the successors, assigns, heirs,
administrators and transferees of the parties.

     10.7 Waivers. The Company and any endorsers, sureties, guarantors, and all
others who are, or may become liable for the payment hereof severally: (a) waive
presentment for payment, demand, notice of demand, notice of nonpayment or
dishonor, protest and notice of protest of this Note, and all other notices in
connection with the delivery, acceptance, performance, default, or enforcement
of the payment of this Note, (b) consent to all extensions of time, renewals,
postponements of time of payment of this Note or other modifications hereof from
time to time prior to or after the maturity date hereof, whether by acceleration
or in due course, without notice, consent or consideration to any of the
foregoing, (c) agree to any substitution, exchange, addition, or release of any
of the security for the indebtedness evidenced by this Note or the addition or
release of any party or person primarily or secondarily liable hereon, (d) agree
that Holder shall not be required first to institute any suit, or to exhaust its
remedies against the Company or any other person or party to become liable
hereunder or against the security in order to enforce the payment of this Note
and (e) agree that, notwithstanding the occurrence of any of the foregoing
(except by the express written release by Holder of any such person), the
Company shall be and remain, directly and primarily liable for all sums due
under this Note.

112527v1

6

--------------------------------------------------------------------------------

10.8      Time. Time is of the essence in this Note.   10.9      Captions. The
captions of sections of this Note are for convenient  

reference only, and shall not affect the construction or interpretation of any
of the terms and provisions set forth in this Note.

     10.10 Number and Gender. Whenever used in this Note, the singular number
shall include the plural, and the masculine shall include the feminine and the
neuter, and vice versa.

     10.11 Remedies. All remedies of the Holder shall be cumulative and
concurrent and may be pursued singly, successively, or together at the sole
discretion of the Holder and may be exercised as often as occasion therefor
shall arise. No act of omission or commission of the Holder, including
specifically any failure to exercise any right, remedy or recourse shall be
effective unless it is set forth in a written document executed by the Holder
and then only to the extent specifically recited therein. A waiver or release
with reference to one event shall not be construed as continuing as a bar to or
as a waiver or release of any subsequent right, remedy, or recourse as to any
subsequent event.

     10.12 No Waiver by Holder. The acceptance by Holder of any payment under
this Note which is less than the amount then due or the acceptance of any amount
after the due date thereof, shall not be deemed a waiver of any right or remedy
available to Holder nor nullify the prior exercise of any such right or remedy
by Holder. None of the terms or provisions of this Note may be waived, altered,
modified or amended except by a written document executed by Holder and then
only to the extent specifically recited therein. No course of dealing or conduct
shall be effective waive, alter, modify or amend any of the terms or provisions
hereof. The failure or delay to exercise any right or remedy available to Holder
shall not constitute a waiver of the right of the Holder to exercise the same or
any other right or remedy available to Holder at that time or at any subsequent
time.

     10.13 Waiver of Trial by Jury. HOLDER AND BORROWER HEREBY KNOWINGLY,
IRREVOCABLY, VOLUNTARILY AND INTENTIONALLY WAIVE ANY RIGHT EITHER MAY HAVE TO A
TRIAL BY JURY IN RESPECT OF ANY ACTION, PROCEEDING OR COUNTERCLAIM BASED ON THIS
NOTE, OR ARISING OUT OF, UNDER OR IN CONNECTION WITH THIS NOTE OR ANY OTHER
DOCUMENT EXECUTED IN CONNECTION THEREWITH, OR ANY COURSE OF CONDUCT, COURSE OF
DEALING, STATEMENTS (WHETHER VERBAL OR WRITTEN) OR ACTIONS OF ANY PARTY HERETO.
THIS PROVISION IS A MATERIAL INDUCEMENT FOR HOLDER TO MAKE THE LOAN EVIDENCED BY
THIS NOTE.

     10.14. This Note is issued, in part, in replacement of the Prior Note. The
indebtedness evidenced by the Prior Note has not been paid; instead this Note is
issued in

112527v1

7

--------------------------------------------------------------------------------

substitution for the Prior Note and the unpaid indebtedness evidenced thereby
continues to be outstanding and is intended to be evidenced hereby.

[signature page follows]

112527v1

8

--------------------------------------------------------------------------------

CECO ENVIRONMENTAL CORP.

By:    /s/ Dennis W. Blazer      Dennis W. Blazer        Title: Vice
President-Finance and Administration  and Chief Financial Officer

Can-Med Technology, Inc. d/b/a Green Diamond Oil Corp.

By: /s/ Phillip DeZwirek

Its: President

112527v1

9

--------------------------------------------------------------------------------