How to Fill a Gap Around Ducts in the Basement

Duct work runs through all homes that have central heating and cooling systems and serves to transport the air to each room in the home. In addition, some ducts provide ventilation to the exterior of the home for exhaust purposes. No matter the purpose, ducts have numerous outlets in a basement area that extend through walls or the ceiling into the living area above. Gaps often exist around the duct which decrease energy efficiency. Filling the gaps requires only inexpensive insulating products.

Tape measure
Silicone caulk
Safety glasses
Disposable latex gloves
Expandable spray foam
Utility knife
Fine-grit sandpaper
Paint (Optional)

Instructions

- 1
  Enter the basement area and locate the area where duct work attaches to the heating or cooling system. Walk along the duct and trace it to where it penetrates a wall or the ceiling of the basement.
- 2
  Locate the gaps around the side of the duct that allow you to see up into the home or to the outside if the duct extends through a wall. Measure the width of the gap with a tape measure.
- 3
  Seal all gaps that are less than 1/4-inch wide by applying a 1/4-inch bead of silicone caulk all the way around them.
- 4
  Put on a pair of safety glasses and disposable latex gloves then shake up a can of expandable spray foam. Screw the plastic tube onto the nozzle of the can.
- 5
  Insert the end of the tube into any gaps that are wider than 1/4-inch and press down on the nozzle to fill them halfway.
- 6
  Wait 12 to 24 hours to allow the foam to dry and expand. Cut off any protruding foam with a utility knife and be careful to avoid cutting into the duct work.
- 7
  Sand the surface of the foam with a piece of fine-grit sandpaper to clean up any rough edges.

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