Two years ago I moved into an 80 year old house with no insulation to speak of. First I tried to insulate all the HVAC ductwork in the unconditioned basement space. I wrapped all the ducts with foil-faced fiberglass and secured the insulation with…. well, duct tape. It didn’t last 12 months. I’d like to do it right this time. What should I be using?
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Well, at the very least use the foil type duct tape instead of the other stuff (which is more properly called DUCK tape, because it's made from duck cloth -- it's not intended for use as duct tape).
found "Shurtape". 2 mil aluminum with a peel-off backing. very sticky stuff. Seems to be working like a charm. Thanks for the headsup.
My first concern before insulation would be sealing all main and side ducts with mastic and something like Polyken mastic tape. Do this on both the supply and return lines. I always thought my ductwork was good. This past summer I sealed it and couldn't believe the the spaces between fittings I found. I then installed oversized fiberglass bats on top. Had 2 X10 joist and used 12" thick material so I had good contact between the subfloor and top of the duct. Around the main duct I constructed a 2 X4 frame and used Tiger Foam and filled it. I then covered the exterior of the frame with 1/2" Thermax and silver taped the joints. This gave me about an R20 around the duct work. On side runs I filled the cavities with fiberglass bats and put a piece of 1/2" Thermax on the bottom. I used caned foam and sealed any holes cut in the subfloor for duct penetrations before insulating them
I've done the mastic and found the foil tape another helpful poster suggested. The remainder of your advice I'll follow after I've installed a new furnace and replaced ALL the duct work (next summer maybe). The current installation looks like it was done by a pack of monkeys: ducts to nowhere, sealed joist spaces used as returns, brand new humidifer installed but no water line run....this house is going to teach me a lot about how to do things correctly. Thanks.
Yes ... just say no to Duct tape ... great for EVERYTHING .... EXCEPT ... ducts.
Use the pressure sensitive tape ... peal and stick - usually has a shiny back/foil face I think (there may be others, though). Use duct mastic - brushed on - comes in gallon cans. There are a number of products out there. Your local sheet metal guy or HVAC outlet should be able to connect you with some good products ... if he has that 'helpful' nature.