In this video, This Old House plumbing and heating expert Richard Trethewey helps a homeowner insulate his ductwork.
Steps for Insulating HVAC Ductwork
- Check the speed of the blower motor on the furnace. If necessary, switch the wires to reduce the blower to its lowest speed.
- Press a continuous strip of foil tape to all longitudinal seams along straight runs of duct.
- Use a paintbrush to apply duct mastic to the joints where an elbow connects to a duct.
- Use a utility knife to cut foil-faced fiberglass insulation to the proper size.
- Wrap the insulation around the duct, and then pinch the seam closed. Secure the insulation with short strips of foil tape.
- Apply a long strip of foil tape along the seam in the insulation. Repeat to insulate the remaining ducts.
- To install preformed duct insulation, start by disconnecting an elbow to expose the end of the duct.
- Snap a plastic cap onto the duct end, then slip the preformed insulation over the duct.
- Gently pull the insulation over the entire length of duct.