# Sealing seams in duct work



## Hugo57 (Mar 28, 2021)

I have been told by the mechanical inspector in Ortonville Michigan. that it is not code to seal the seams and connections in the furnace air conditioning ductwork .according to what I read in the 2015 building code it is mandatory is this true. This is metal ductwork my last two houses had taped seams


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## rogerpa (Mar 28, 2021)

MRC 2015

N1103.3.2 (R403.3.2) Sealing (Mandatory).
*Ducts, air handlers and filter boxes shall be sealed*. Joints and seams shall comply with either the International
Mechanical Code or Section M1601.4.1 of this code, as applicable.
Exceptions:
1. Air-impermeable spray foam products shall be permitted to be applied without additional joint seals.
2. For ducts having a static pressure classification of less than 2 inches of water column (500 Pa), additional closure
systems shall not be required for continuously welded joints and seams, and locking-type joints and seams of other
than the snap-lock and button-lock types.

M1601.4.1 Joints, seams and connections.
Longitudinal and transverse joints, seams and connections in metallic and nonmetallic ducts shall be constructed as
specified in SMACNA HVAC Duct Construction Standards—*Metal and Flexible and NAIMA Fibrous Glass Duct
Construction Standards. Joints, longitudinal and transverse seams, and connections in ductwork shall be securely
fastened and sealed *with welds, gaskets, mastics (adhesives), mastic-plus-embedded-fabric systems, liquid sealants or
tapes. Tapes and mastics used to seal fibrous glass ductwork shall be listed and labeled in accordance with UL 181A
and shall be marked “181A-P” for pressure-sensitive tape, “181 A-M” for mastic or “181 A-H” for heat-sensitive tape.
Tapes and mastics used to seal metallic and flexible air ducts and flexible air connectors shall comply with UL 181B
and shall be marked “181 B-FX” for pressure-sensitive tape or “181 BM” for mastic. Duct connections to flanges of air
distribution system equipment shall be sealed and mechanically fastened. Mechanical fasteners for use with flexible
nonmetallic air ducts shall comply with UL 181B and shall be marked 181B-C. Crimp joints for round metallic ducts
shall have a contact lap of not less than 1 inch (25 mm) and shall be mechanically fastened by means of not less than
three sheet-metal screws or rivets equally spaced around the joint.
Closure systems used to seal all ductwork shall be installed in accordance with the manufacturers’ instructions.
Exceptions:
1. Spray polyurethane foam shall be permitted to be applied without additional joint seals.
2. Where a duct connection is made that is partially inaccessible, three screws or rivets shall be equally spaced on the
exposed portion of the joint so as to prevent a hinge effect.
3. For ducts having a static pressure classification of less than 2 inches of water column (500 Pa), additional closure
systems shall not be required for continuously welded joints and seams and locking-type joints and seams of other than
the snap-lock and button-lock types.


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## Hugo57 (Mar 29, 2021)

Thanks that’s what I thought. Got to go over this guys head some how. To get this job done right


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## tmurray (Mar 29, 2021)

Wait. It's not code meaning the code is silent and thus does not regulate it, or that the code specifically prohibits the sealing of ductwork?

If it is silent, then the inspector shouldn't care, so I am guessing that they think the code prohibits it. 

You may want to simply ask for a code section from him instead of going over their head right from the start. It is a lot easier to admit I am wrong to a contractor than to a contractor and my boss. There is a lot more ego at risk in the second scenario and there is a much stronger likely hood that they will dig in more. 

If they are a "good' inspector, they should relent when they can't find a code section to support them. If they are not a good inspector, you will have to go over their head anyway.


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## klarenbeek (Mar 29, 2021)

You may want to check and see if they have any local ordinances that change sealing requirements....


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