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Insulating furnace supply plenum -- what materials?

blueman Member Posts: 11
The only part of our high efficiency gas furnace system that is "leaking"  significant heat appears to be the (uninsulated) sheet metal supply plenum.

I would like to insulate it and was wondering what types of insulation would be best?

My initial thought was to use some type of foil-backed rigid foam insulation like the type available at the big box stores.

But I want to make sure that there are no general safety or code issues determining the insulation type given that it is near the furnace.

(Also, of course, I will be monitoring basement temperatures to make sure it doesn't do too good a job of keeping heat out of the basement...)


  • Al Letellier_21
    Al Letellier_21 Member Posts: 402
    supply plenum insulation

    DO NOT USE rigid foam insulation unless you know what the temperature rating is. Ductwork is typically insulated with foil or vinyl backed fiberglass insulation specially made for the application. Get professional help before you either cause sickness from fumes or fire from underrated insulation. Nothing to fool around with here.
  • blueman
    blueman Member Posts: 11
    So, is there a specific insulation type you recommend

    That's why I was asking -- to understand what the appropriate insulation to use is given the temperature of the plenum and the proximity to combustion chamber. I mentioned rigid foam, because I'm pretty sure I have seen it in professional installations but wanted to be sure about temperature rating, etc.

    I hardly think I need to bring in a professional to do the installation but I do want to make sure I am using the right materials that will be safe, effective, and professional-looking. But thanks for the warning anyway...
  • Insulating furnace supply plenum

    Did mine 15 yrs ago with hardboard foil fiberglass. (foil on outside), still there, never a prob!
  • Al Letellier_21
    Al Letellier_21 Member Posts: 402
    plenum insulation

    Didn't mean to say you couldn't do the work, just wanted to make sure it was done safely...consult a local insulation supplier or HVAC guy for the best stuff to use. I also sub out insulation work but have used fiberglass duct wrap with foil face with goo success.
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