How to Seal a Heating Duct

If your heating ductwork springs a leak, it will affect your home's energy efficiency. Forced heat will flow into the attic above the ceiling, and because hot air rises, it will dissipate up into the roof. This will cause your central air conditioning unit or heater to run continuously, as the thermostat inside your home will not indicate the set temperature setting has been reached. You'll need to seal the duct immediately to fix the problem.

Dish soap
Spray bottle
Rags
Household cleaner
Mastic sealant
Brush
Aluminum tape

Instructions

- 1
  Squirt dish soap into a spray bottle and fill with water. Go to your heat duct and spray it while the system is on. Look for bubbles to form to locate the leak.
- 2
  Clean the duct where the leak is occurring using rags and a household cleaner. Get as much of the dirt and dust off the heat duct as possible.
- 3
  Apply mastic sealer over the leak on the heat duct with a brush. Allow the mastic to set in for 10 to 15 minutes and then apply a second coat of mastic sealant on the heat duct. Wait another 10 to 15 minutes.
- 4
  Wrap the heat duct in aluminum tape, covering the leak and mastic sealant completely. Stretch the aluminum tape tightly around the heat duct to keep it free of wrinkles and air bubbles.

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