Air sealing and insulating ductwork
conor_mc
| Posted in Mechanicals on
I’m planning on air sealing and insulating the forced air ductwork in my house. The work will likely mean temporarily disassembling the ductwork. My ductwork has the old school leaky takeoffs. Would it be worth it to replace those with air-tight takeoffs or should I just slather mastic all over the old style and call that good?
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Replies
If the duct work is in the conditioned space sealing it will have zero effect on your operating costs and modest effects on comfort at best.
If for some silly reason the duct work is in the unconditioned space Try to find a way to move the ducts inside the conditioned space if at all possible.
If you find yourself stuck with silly you will find this article helpful.
https://www.greenbuildingadvisor.com/article/ducts-in-an-unconditioned-attic#:~:text=There%20are%20two%20options%20for,balance%20of%20the%20attic%20unconditioned.
Walta
Thanks Walta. These particular ducts are underneath my first floor which means it's mostly in my conditioned zone of my house. But I still don't particularly need to heat up my floor joists and the deep insulation in those bays. It's not a lot of money to buy the tape, mastic, and insulation and luckily my time is free!
Being in the conditioned space it really does not matter all the BTU stay inside the envelope and will distribute themselves pretty evenly.
I do like the foil tape on ductwork but it is important to clean the old ductwork before installing it.
You time would be better spent finding and fixing leaks in your thermal envelope.
Walta
I agree with Walta that sealing up leaky ductwork usually doesn't gain you much in terms of overall energy efficiency. If you want to seal things, duct mastic is often better than foil tape, and it can seal up things without need of dissassembly.
I like to use foil tape on new clean stuff, since it's quick and clean. I use Nashua 324A "real" metal foil tape for this. I prefer duct mastic on pretty much everything else, especially old stuff that's hard to reach. With mastic, you can just smear on a layer of the stuff and be done -- you usually don't need to clean the duct much (within reason), and it can seal around leaky boots and other akward stuff that is very difficult to seal well with tape.
Bill
Thanks for the info!
Bill would you consider editing this line to indicate that we are talking about ductwork inside the conditioned space.
“I agree with Walta that sealing up leaky ductwork usually doesn't gain you much in terms of overall energy efficiency”
As leaky ductwork in a vented attic or crawlspace are huge energy efficiency concerns.
Walta