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Discussion Starter #1
What is the best/correct way to insulate through floor register boots?

My first floor ducting is in the unconditioned crawlspace. The existing 4x12 metal boots are between the floor joists with fiberglass insulation stuffed around them.

Has anyone ever had the boots spray foamed by an insulation company? That seems like a good way to insulate the metal and seal the through floor penetration.
 

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Better to seal the boot with caulk. I wouldn't spray foam the boots. Incase you ever need to redo the floor.
 

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Hi BT,

I understand you point on the caulk but what about the metal boot? Shouldn't the boot be insulated with something better than fiberglass insulation loosely placed around the metal?

Due to the temperature and humidity differences between the conditioned air in the duct and the unconditioned crawlspace, wouldn't that cause the metal to sweat if not properly insulated?
 

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Foil wrapped insulation works fine, and the pipe and boot joints should of course all be sealed before wrapping. If you want to use spray foam for sealing the pipe and boot to the pipe, that works better. But can be more expensive and harder to do.
 
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