Assembling Ductwork For Range Hood

sequoia_2007September 23, 2013

I am running 7 inch round 26 gauge metal duct for our kitchen and assembling five 3 foot sections for a long run.

When I align all the seams I find one seam on top of another forces the walls of the mating ducts apart significantly. Would it be better rotate the mating ducts so the seams are four inches apart? I find doing this reduces the distortion of the duct walls.

In addition, I am using three #8x1/2â screws to secure the mating ducts together and sealing the joint with UL Listed metal duct tape. Should the seams that run along the length of the pipe be sealed also with tape?

Thank you for taking the time to read my post and consider my questions.

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kaseki

I am not a duct specialist, but wonder if those ducts are suitable for their purpose. If I had to use them, I would certainly seal any gaps.

However, first I would use a sheet-metal crimping tool to slightly decrease the male end diameter.

The requirement for steel ducting is to reduce risk of a grease fire spreading to house structures. Gaps do not help achieve this goal.

kas

    Bookmark   September 24, 2013 at 8:52AM
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cookncarpenter

Yes, it helps if you rotate and stagger the seams for a better fit.
I've never seen a HVAC installer tape the long seams, but I guess it couldn't hurt.

    Bookmark   September 24, 2013 at 9:58AM
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sequoia_2007

Thanks. I offset the seams by three inches and inserted one of the three screws securing each section between the offset seams. I used Polyken 339 to seal the sections and seams. I used CCWI-181 on the 90 degree elbow seams.

http://polyken.com.mx/Archivos%20Polyken/PDF/Industriales%20Trad/Fichas%20Tecnicas/FICHA%20TECNICA%20339.pdf

http://www.ductoutlet.com/CCWI_181_Duct_Sealant_1Gal_p/ccwi-181.htm

    Bookmark   September 24, 2013 at 11:15PM
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