[HONEYWELL INC. LETTERHEAD]
 
                                                                     EXHIBIT 5.1
 
Board of Directors
Honeywell Inc.
Honeywell Plaza
Minneapolis, Minnesota 55408
 
Ladies and Gentlemen:
 
    I am Vice President and General Counsel of Honeywell Inc., a Delaware
corporation (the "Company" or the "Guarantor"), and the parent company of
Honeywell Finance B.V., a private limited liability corporation organized under
the laws of The Netherlands ("Honeywell B.V.") and Honeywell Canada Limited, a
corporation incorporated under the laws of the Province of Ontario, Canada
("Honeywell Canada") (the Company, Honeywell B.V. and Honeywell Canada are
sometimes referred to individually as an "Issuer"). The Company, Honeywell B.V.
and Honeywell Canada propose to issue from time to time up to U.S. $600,000,000
aggregate principal amount of debt securities (the "Debt Securities") pursuant
to a Registration Statement on Form S-3 (the "Registration Statement"). The Debt
Securities offered by Honeywell B.V. and Honeywell Canada will be
unconditionally guaranteed as to principal of and any premium and interest by
the Company (the "Guarantee"). The Debt Securities of the Company will be issued
under an Indenture (the "Company Indenture") in the form filed as Exhibit 4.1 to
the Registration Statement, and the Debt Securities of Honeywell B.V. and
Honeywell Canada will be issued under an Indenture (the "Subsidiary Indenture")
in the form filed as Exhibit 4.2 to the Registration Statement (the Company
Indenture and the Subsidiary Indenture are sometimes collectively referred to as
the "Indentures").
 
    I have examined such documents, including resolutions of the Board of
Directors of the Company adopted on April 15, 1997, resolutions of the
Shareholders of Honeywell B.V. adopted on August 15, 1997, and resolutions of
the Board of Directors of Honeywell Canada adopted on August 15, 1997
(collectively, the "Resolutions"), and have reviewed such questions of law, as I
have considered necessary and appropriate for the purposes of the opinions set
forth below. In rendering the opinions set forth below, I have assumed the
authenticity of all documents submitted to me as originals, the genuineness of
all signatures and the conformity to authentic originals of all documents
submitted to me as copies. I have also assumed the legal capacity for all
purposes relevant hereto of all natural persons and, with respect to all parties
to agreements or instruments relevant hereto other than the Company, that such
parties had the requisite power and authority (corporate or otherwise) to
execute, deliver and perform such agreements or instruments, that such
agreements or instruments have been duly authorized by all requisite action
(corporate or otherwise), executed and delivered by such parties and that such
agreements or instruments are the valid, binding and enforceable obligations of
such parties. As to questions of fact material to this opinion, I have relied
upon certificates of officers of the Company and of public officials.
Capitalized terms used herein and not otherwise defined herein shall have the
meanings assigned to them in the Indentures incorporated by reference as
Exhibits 4.1 and 4.2 to the Registration Statement.
 
    Based on the foregoing, I am of the opinion that:
 
        1.  When the specific terms of a series of Debt Securities of the
    Company have been specified in a supplemental indenture or an Officer's
    Certificate of the Company, which has been executed and delivered to the
    Trustee by an officer of the Company authorized to do so by the Resolutions,
    such series of Debt Securities will have been duly authorized by all
    requisite corporate action and, when

The Board of Directors
Honeywell Inc.
August 18, 1997
Page 2
 
    executed and authenticated as specified in the Company Indenture and
    delivered against payment therefor pursuant to the terms described in the
    Registration Statement and as specified by an officer of the Company
    authorized to do so by the Resolutions, will constitute valid and binding
    obligations of the Company, enforceable in accordance with the terms of such
    series.
 
        2.  When the specific terms of a series of Debt Securities of an Issuer
    and the Guarantor have been specified in a supplemental indenture or an
    Officer's Certificate of the applicable Issuer thereof and the Guarantor,
    which has been executed and delivered to the Trustee by an officer of the
    applicable Issuer thereof and the Guarantor authorized to do so by the
    Resolutions, such series of Debt Securities of such Issuer and the related
    Guarantee will have been duly authorized by all requisite corporate action
    and, when executed and authenticated as specified in the Subsidiary
    Indenture and delivered against payment therefor pursuant to the terms
    described in the Registration Statement and as specified by an officer of
    such Issuer and the Guarantor authorized to do so by the Resolutions, such
    series of Debt Securities and the related Guarantee will constitute valid
    and binding obligations of such Issuer and the Guarantor, respectively,
    enforceable in accordance with the terms of such series.
 
    The opinions set forth above are subject to the following qualifications and
exceptions:
 
           (a) The opinions are subject to the effect of any applicable
       bankruptcy, insolvency, reorganization, moratorium or other similar law
       of general application affecting creditors' rights.
 
           (b) The opinions are subject to the effect of general principles of
       equity, including (without limitation) concepts of materiality,
       reasonableness, good faith and fair dealing, and other similar doctrines
       affecting the enforceability of agreements generally (regardless of
       whether considered in a proceeding in equity or at law).
 
           (c) In rendering the opinions set forth above, I have assumed that,
       at the time of the authentication and delivery of a series of Debt
       Securities of an Issuer (and the related Guarantee, if applicable), the
       Resolutions referred to above will not have been modified or rescinded,
       there will not have occurred any change in the law affecting the
       authorization, execution, delivery, validity or enforceability of such
       series of Debt Securities (and the related Guarantee, if applicable), the
       Registration Statement will have been declared effective by the
       Commission and will continue to be effective, none of the particular
       terms of such series of Debt Securities (and the related Guarantee, if
       applicable) will violate any applicable law and neither the issuance and
       sale thereof nor the compliance by the applicable Issuer or the
       Guarantor, if applicable, with the terms thereof will result in a
       violation of any agreement or instrument then binding upon such Issuer or
       the Guarantor or any order of any court or governmental body having
       jurisdiction over such Issuer or the Guarantor.
 
           (d) As of the date of this opinion, a judgment for money in an action
       based on a Debt Security denominated in a foreign currency or currency
       unit in a federal or State court in the United States ordinarily would be
       enforced in the United States only in United States dollars. The date
       used to determine the rate of conversion into United States dollars of
       the foreign currency or currency unit in which a particular Debt Security
       is denominated will depend upon various factors, including which court
       renders the judgment. Under Section 27 of the New York Judiciary Law, a
       state court in the State of New York rendering a judgment on a Debt
       Security would be required to render such judgment in the foreign
       currency or currency unit in which such Debt Security is denominated, and
       such judgment would be converted into United States dollars at the
       exchange rate prevailing on the date of entry of the judgment.

The Board of Directors
Honeywell Inc.
August 18, 1997
Page 3
 
    My opinions expressed above are limited to the laws of the State of New
York, the Delaware General Corporation Law and the federal laws of the United
States of America, and I am expressing no opinion as to the laws of any other
jurisdiction. With respect to matters of Canadian law you are being provided
with the opinion, dated the date hereof, of Baker & McKenzie, Canadian counsel
to the Company and Honeywell Canada. With respect to matters of Dutch law you
are being provided with the opinion, dated the date hereof, of Nauta Dutilh,
Dutch counsel to the Company and Honeywell B.V.
 
    I hereby consent to your filing this opinion as an exhibit to the
Registration Statement and to the reference to me under the caption "Validity of
Debt Securities and Guarantee" contained in the Prospectus included therein.
 
                                          Very truly yours,
 
                                               /s/ EDWARD D. GRAYSON, ESQ.
 
                                          --------------------------------------
 
                                                 Edward D. Grayson, Esq.
 
Dated: August 18, 1997