Insulating ductwork
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What is the best way to insulate HVAC ductwork in an unconditioned space?
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Replies
The best way is to convert the space into conditioned space, air sealing and insulating the space, but that's not necessarily going to be cost effective.
More information is needed on both the ducts and the space to come up with optimal solutions on insulating the ducts themselves.
The ductwork in question is for a 450 sq ft addition cantilevered over a 350 sq ft concrete block garage/foundation. The addition consists of an entry hall, bathroom, and master bedroom, all connected by a hallway. The heat source is a ducted mini split with: master bedroom--3 supply & 1 return; bath--1 supply & 1 return; hall--1 supply & 2 returns. In the basement the ceilings are 92 inches with the air handler and un-insulated ductwork suspended from the ceiling. This minisplit unit just does not heat things up adequately. The outside temp went down below zero recently and the indoor temp couldn't get above 50F.
I could possibly box in most of the ductwork. What about just boxing in the supply ducts with 1 or 2 inches of Thermax or some heavy duty insulation sheathing? Would stuffing the box with extra fiberglass batts be helpful?
HI Brian -
Dana is the GBA Q&A go-to HVAC guy and he will in all liikelihood give you a better answer if you give us (him) better information for your question. He is incredibly generous to the GBA Q&A community.
And I think he would agree that just as with building enclosures, duct performance is a key combination of the airtightness and insulation of the HVAC ducts. Air leakage in ducts is a double problem of inefficiency and pressure imbalance potential, with added consequences regarding indoor air quality and even combustion safety.
Peter
The very best answer is to not insulate the duct at all and eater eliminate the ducts or moves them inside the conditioned space where no insulation is necessary.
Walta