# Insulating HVAC Duct Register Boots



## TeeRiddle (Oct 21, 2014)

Hi all,

Not sure if this topic belongs here or in the HVAC section, but figured I'd start here.

While in my crawlspace last summer I noticed one of my sheet metal duct register boots was not insulated and was sweating a lot, so much so that the plywood subfloor around the boot was soaking wet. I didn't check them all, but I'm sure if one is like this the rest are probably the same.

What's the best way to insulate the boots to prevent the condensation? What kind of insulation should I use? And should I use mastic or the metal foil tape to seal?

Thanks!


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## akjose (Jan 1, 2013)

Not sure how these insulated duct boots are tapped for the pipe coming in. Hard to tell from the pictures. It would be one option. I have seen duct boots spray foamed to seal from the gap between register and floor as well as to insulate the boots. shouldn't take much to do each register.

http://www.homedepot.com/p/8-in-x-4-in-Duct-Board-Insulated-Register-Box-R6-DIRB8X4/100135701


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## Windows on Wash (Aug 30, 2011)

+1

Spray foam is going to be your best bet for complete coverage and proper air seal.


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## TeeRiddle (Oct 21, 2014)

Thank you for the replies! Do you mean the Great Stuff type spray foam or something else?


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## akjose (Jan 1, 2013)

Tiger foam (online)
Foam it green (online)
FrothPak 200, FrothPak 600 (sold at lowes)

The tiger and foam it green brands come in a larger package and get more for your money. 

Great stuff would take alot of cans. Complete coverage of the metal, gaps, and cracks is what you want.


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## Windows on Wash (Aug 30, 2011)

+1 to the above post.

You need a froth pak and for it to be a sprayable foam (2 part) vs. straw foam.


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## Gary in WA (Mar 11, 2009)

Precaution; make sure the boot is fastened all around the perimeter of the hole or you will blow it in and have a heck of a mess of foam. All the joints (including unused elbows) should be taped/mastic or just sticky taped, then insulated with at least (code minimum) duct insulation R-6-8 in your unconditioned crawlspace. IMO, just wrap/tape some duct FG insulation around it- if accessible, when a lot of them are on outside walls (close clearances)- are not, then SPF works better. You could also build a rigid foam box around it first, then SPF from a can.

If you don't fasten it well, the tin will flex stopping the register grate from fitting inside... and it will ride-up and sit higher than before your work. http://www.carb-swa.com/Collateral/Documents/CARB-SWA/Guides/Sealing_and_Insulating_Ducts.pdf

Gary


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