Duct insulation in conditioned attic
connorkatz
| Posted in General Questions on
Hi all,
I am about to install insulation on my ducts in a conditioned attic .
Very air tight 4in polyiso exterior r30 batt interior zone 3, system is designed with calced supply for attic.
My question is, would I get any real world value out of doing an r6 or r8 fiberglass insulation for the ducts, over a basic bubble foil wrap (rNotMuch)
I am leaning towards the bubble foil as its cheaper and easier to install, but I am wondering what if anything I would lose by not installing fiberglass insulation?
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Replies
Insulating ducts in a truly conditioned attic will save zero energy. At best you might change the discharge temp a tenth of a degree.
If you are not really going to condition the attic by installing supply and return registers in the attic and “encapsulate” the attic and let it be at whatever temp and humidity it wants to be. In that case the insulation could save some energy but you would be playing a very risky game.
Walta
Walta has some good points. I'm in zone 5 with hot humid summers and all ducting inside conditioned space is not insulated. About the only time you get any condensation on the outside of the ducting if all the doors and windows are left open in the middle of the summer with the AC running.
The one I disagree with that conditioned attics are risky. With your assembly of 4" exterior rigid in zone 3, no surface will ever get cold enough to have moisture issues. Add in there the fact that you have supply register, you'll be fine.
I don't see much point with beefy insulation in a conditioned attic either. Since the attic is inside the home's envelope in this situation, "losses" from the ductwork still heat (or cool) the interior of the home. This would be different in a vented attic, where those same losses would be "lost" to the outdoor air where they are wasted.
If you want to do anything, I'd try something light like the bubble stuff, which is probably around R1-R2 or so. I don't think it's really worth doing though, unless you're trying to limit condensation on the ducts during cooling season.
Bill
Thanks guys, we get pretty darn hot here is Paso Robles, CA 100+ during the summer months, so I wanted to add at least something (bubble foil) on the ducts just as an extra (hopefully overkill) layer of safety for condensation.