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Old 09-12-2010, 06:58 PM
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Ive got an old furnace and there is no insulation on the duct work. What is the recommended R level for insulation I should use? I live in Connecticut where it can get very cold to very hot depending on time of year.

The duct on top of the furnace/blower is flat. I havent found a good range of choices of sheathing to use. I wanted to use 3/4 inch but that only gets me about a 3 R level. Id think I would want something higher than that. I really didnt want to use 2 inches worth just to get a 10 R level. Does anyone know of anything with a higher R level but small thickness?

Also, the duct that takes air from the house, should that be insulated as well?
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Old 09-13-2010, 06:52 AM
Location: Johns Creek, GA
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Look at the section "Duct Wrap":


It will give you a couple of charts about "R" values and "K" values, acoustic values, etc. Those values will be pretty much the same regardless of manufacturer.

On the old metal type duct work, return lines were generally not insulated. Of course with today's flex duct being used it would be. THe main advantage to insulating a return of your type would be mainly for acoustical purposes.
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Old 09-22-2010, 04:37 PM
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Thanks K'ledge

I want to insulate my air handler. Ive started insulating the duct work with wrapping. I was thinking of using sheathing for the air handler. Any recommendations other than sheathing?
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Old 09-22-2010, 06:36 PM
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Default If duct work is in "temperate conditioned" space...

The value of insulating the ductwork that is heated / colled space is minimal, and if your use lightweight rigid sheeting or foam odds are high you will have acoustic issues.

Now it the ducts are passing through unheated / uncooled space then I would strongly recommend using as much high quality insulation as you can get around those ducts. While it might create a problem for future service / renovation I would suggest spray on closed cell foam, as much the company can pump...
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Old 09-22-2010, 08:55 PM
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If you wrap the ducts make sure they are properly sealed, mastic works well. If you spray foam that's a all-in-one product that insulates and seals. I'd recommend spray foam if you don't think you'll be replacing the ducts anytime soon. You also may want to make sure that all your rooms are evenly heated/cooled which means the ducts are properly sized for your home.
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