Step 1
Remove old or damaged ducting insulation with heavy duty cutting shears. Many outside ducts have the wrong kind of insulation on them and are probably not weather resistant.
Step 2
Scrape off any remaining insulation pieces, glue or tape residue with the putty knife.
Step 3
Clean the duct area with the degreser and clean rags. The new ducting insulation won't stick well unless the surface is clean.
Step 4
Install new, foil-style duct insulation, which comes in rolls that are different lengths and widths and that has a foil backing on both sides with air pockets in-between. The R-value on foil-backed duct insulation is usually 6.5 or higher, making it a good choice for outside ducting.
Step 5
Start at one end, and wrap the foil-backed duct insulation around the ducting. Use overlapping wraps as you go from one end of the duct to the next. Use metal tape to seal any seams. It has a sticky back and is specially designed for duct sealing. It tears off of the roll just like duct tape does.
Step 6
Cut any corner seams with the heavy duty cutting shears. Cut them at a 45-degree angle. Use the metal tape to close the cut seams. Overlap the coner seams a bit to make certain no leaks occur.
Step 7
Install heavy plastic sheeting over any ducts exposed more directly to rain or snow. Staple the heavy plastic sheeting to the walls and the bottom of the roof overhang.