How to Insulate Furnace Ducts Under a Mobile Home

Turn on the furnace system so that air flows through the external ducts. Crawl under the mobile home, detaching a section of skirting if required. Move along the entire furnace duct, which runs the length of the mobile home, and feel it with your hands to locate any leaks. Mark any leaks using a black marker.

Open a tub of water-soluble mastic and insert a paintbrush into it. Cover all leaky areas with the mastic, extending it one inch beyond the leaks.

Cut pieces of fiberglass mesh tape the same size as the leak areas using scissors. Press the tape into the mastic and wait until the mastic dries completely.

Move to one end of the furnace duct and wrap a piece of duct wrap insulation with an R value of 6 around it. Ensure the foil or paper side faces outward. Trim off the excess insulation using a utility knife and then secure the free edges using foil-backed tape.

Wrap a second piece of insulation batting around the duct, butting the end up snuggly against the first piece. Trim the excess insulation and secure the free ends with foil tape. Wrap additional foil tap around the seam between the first and second pieces of insulation.

Repeat the process along the entire length of the duct work until it is entirely insulated.