Insulating crawl space HVAC ducts


Old 06-10-04, 12:17 PM
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Question Insulating crawl space HVAC ducts

My crawl space is damp and dirty. I read with keen interest the posts about insulating between the floor joists, and about installing a 6mm vapor barrier.

I need some insights about what to do about my very old HVAC ducts in the crawl space. Like the insulation on the floor, the insulation around the HVAC ducts has withered and fallen off to where the ducts are pretty much bare exposed metal. No doubt, there is a plume of heat emanating from my house in the winter and I am singlehandedly contributing to global warming.

Now I'd like to reinsulate the ducts. No contractor has found this job big enough, nor pleasant enough (the crawl space is not a nice place to be) to bid on it.

I'd like to be able to raise the temperature in the house in winter, and certainly to be able to cool it more than I seem to in the hot summers.

What is the best way to insulate the ducts? They are, for the most part, difficult to wrap as there is no clearance between them and the floors above.

Thanks in advance!
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Old 06-10-04, 01:09 PM
Ed Imeduc's Avatar
Join Date: Aug 2002
Location: Mountain Williams Missouri
Posts: 18,389

DONT DONT DONT. let the ducts alone. get that insulation out of the floor joist. Put a 6 mil poly on the ground. over lap it 2' tape all seams up the wall 1' . Put 2" or 3" polystyrene on the wall up to the floor joist. Put a R19 insulation in just the joist space up there on the sill plateall around the home.put one are two small registers in the duct to let some air out down there.
This will dry it out down there. It also works like a heat sinkand give you a warm floor. Any home that we have done this way or reworked this way have had much lower fuel bills.

Old 06-11-04, 01:35 AM
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Smile Crawl space resources

Thanks for the amazingly fast response, Ed.

Allow me to also plagiarize an earlier thread of yours for the benefit of others. You had referred to two helpful resources, which are really good for us novices, in that they include pictures of the suggested approaches (vapor barrier installation etc.)

These are:


Now... if only I had stumbled on this site a few years back...

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