EXHIBIT 3.21
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                                                               State of Delaware
                                                              Secretary of State
                                                        Division of Corporations
                                                         Filed 9:00 AM 8/22/2000
                                                              0014 25777-3278169


                          CERTIFICATE OF INCORPORATION

                                       OF

                           NAPCO WINDOW SYSTEMS, INC.

         FIRST:   The name of the Corporation is Napco Window Systems, Inc.

         SECOND:  The registered office of the Corporation in the State of
Delaware is located at 1013 Centre Road, City of Wilmington, County of New
Castle. The name and address of its registered agent is Corporation Service
Company, 1013 Centre Road, Wilmington, Delaware 19805.

         THIRD:   The purpose of the Corporation is to engage in any lawful act
or activity for which corporations may be organized under the General
Corporation Laws of the State of Delaware.

         FOURTH:  The total number of shares of stock which the Corporation
shall have authority to issue is Three Thousand (3,000) shares of Common Stock
of the par value of One Cent ($.01) per share.

         FIFTH:   The name and mailing address of the Incorporator is Dawn M.
Urbanowicz; Nortek, Inc.; 50 Kennedy Plaza; Providence, RI 02903.

         SIXTH:   The Corporation is to have perpetual existence.

         SEVENTH: Elections of Directors need not be by written ballot unless
the by-laws of the Corporation so provide.

         EIGHTH:  In furtherance and not in limitation of the powers conferred
by the laws of the State of Delaware, the Board of Directors of the Corporation
is authorized and



empowered to adopt, alter, amend and repeal the by-laws of the Corporation in
any manner not inconsistent with the laws of the State of Delaware.

         NINTH:   The Corporation shall indemnify its officers, directors,
employees and agents to the fullest extent permitted by the General Corporation
Laws of Delaware.

         TENTH:   Meetings of stockholders may be held within or without the
State of Delaware, as the by-laws may provide. The books of the Corporation may
be kept (subject to any statutory provision) outside the State of Delaware at
such place or places as may be designated from time to time by the Board of
Directors or in the by-laws of the Corporation.

         ELEVENTH: The Corporation reserves the right to amend, alter, change or
repeal any provision contained in the Certificate of Incorporation, in the
manner now or hereafter prescribed by statute.

         TWELFTH: A director of the Corporation shall not be liable to the
Corporation or its stockholders for monetary damages for breach of fiduciary
duty as a director, except to the extent such exemption from liability or
limitation thereof is not permitted under the Delaware General Corporation Law
as the same exists or may hereafter be amended. No amendment or repeal of this
Article TWELFTH shall apply to or have any effect on the liability or alleged
liability of any director of the Corporation for or with respect to any acts or
omissions of such director occurring prior to such amendment or repeal.

         I, THE UNDERSIGNED. being the incorporator hereinbefore named, for the
purpose of forming a corporation pursuant to the General Corporation Laws of the
State of Delaware, do make this certificate, hereby declaring and certifying
that this is my act


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and deed and the facts herein stated are true, and accordingly have hereunto set
my hand this 22nd day of August, 2000.


                                    Dawn M. Urbanowicz
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                                    Dawn M. Urbanowicz


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