We have several high efficiency gas furnaces. The furnace itself is
cool to the touch as are the insulated ducts. The only warm-to-hot part
is the sheet metal supply plenum that is uninsulated.

Since the furance is in our unfinished basement, it seems logical to
insulate the plenum right?

- Would a water heater blanket work well to insulate the plenum?
- Any other suggestions for insultating material? (I know regular
fiberglass batts are cheaper but I don't know if they are rated for
contact with a supply plenum)?

Also as a related question, we have a circa 2003 water heater who
outside is barely warm to the touch (if at all). Would there still be
any measurably signiicant benefit to wrapping it in a water heater
blanket or is it already well insulated enough?


*There is insulation made for ducts. You can usually buy a roll at a
plumbing supply. I have seen small rolls at Home Depot.