Insulate supply duct

BlueBSH · 12-29-2009, 04:10 PM

While taping up all the seams on the sheet metal duct work with foil tape to close off some of the hot air loss I was having (after got that done the basement dropped 20 degrees... not kidding... there was also some holes that needed sheet metal covered over them when small metal pieces where corners on the supply duct was... the HVAC people that did the duct work must of been incompetent... anyways)... I still seem to be loseing a lot of heat because of it radiating from the metal supply duct that runs 10 ft one direction from the furnance then another 50 ft the other direction... the 50 ft part is in conditioned space... the furnance and 10 ft the other way are in unconditioned space... is there anything I can do to insulate these that doesnt cost a ton? someone at lowes suggested this metalic looking bubble wrap like stuff that claims its R4.5 insulation that you wrap around the duct then foil tape the seams...

any suggestions?

Edit: Reflectix is what they sell at lowes

SPS-1 · 12-29-2009, 06:13 PM

I put the "bubble wrap" insulation on a section of round duct. See attached picture. The instructions said to spiral it onto the duct, but I put it in 16" sections with no overlap, just because I think it looks better this way. Secured with aluminum duct tape. There is an axial seam on the "bubble wrap", but I rotated the wrap so that it is not visible. It was fast to put up, and looks decent. If you are looking for higher R value, google "Mcmaster Carr Supply" and then do a search for "duct insulation". Advance through the pages, because they will have several pages of insulation literature.

SPS-1 · 12-29-2009, 07:21 PM

The furnace was just running. The section of duct with bubble wrap is somewhat cooler than the section without it. But if you want to really stop heat transfer, you can surely find higher R value insulation.

veesubotee · 12-30-2009, 04:17 PM

Reflectix has an R value of 3. If you first wrap 2 turns of approx 1.5" wide on the duct, every 2 running feet before wrapping the duct, it will provide an air space and increase the R value to 6.

I found after having a modulating furnace installed, running mostly at very slow speed (great for comfort), caused a great deal of heat to be lost to the basement. After wrapping the trunks, heat loss has been eliminated; air temperature at farthest register is several degrees hotter and basement is a little cooler.