How to Insulate a Square Duct

Square or rectangular-shaped metal ducts are used to distribute hot air from a furnace and cool air from an air conditioner in homes with forced-air HVAC systems. The ducts travel throughout the house, branching off to blow the air into different rooms through vents. You can make the ducts more energy-efficient by enclosing them in rolled-fiberglass insulation, which prevents them from emitting and absorbing heat from the surrounding air.

Tape measure
Rolled fiberglass insulation
Utility knife
Gloves
Safety goggles
Mask or respirator
Metallic foil tape

Instructions

- 1
  Measure and add together the four sides of each duct, and add 3 inches to the total so the insulation isn't pulled tightly against the duct. Fiberglass insulation is less effective when compressed.
- 2
  Cut strips of insulation to fit your measurements with a utility knife. Wear gloves, safety goggles and a mask or respirator when handling the fiberglass.
- 3
  Cut a strip of metallic foil tape to match the width of the insulation. Place the tape against the foil side of one end of the insulation. Position the tape so only half is against the foil and the other half is exposed.
- 4
  Wrap the insulation around the first part of the duct. Bring the two ends together, and press the exposed half of the foil tape over the other end of the strip of insulation to secure the strip around the duct.
- 5
  Continue to install insulation until the ducts are complete.
- 6
  Place metallic foil tape over the seams between the different strips of insulation to further insulate the duct.

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