How to Seal AC Ducts

If your utility bills seem unusually high in the summer, or if you notice that your air conditioning doesn't seem to properly cool your home, you may have leaks in the ductwork. Any loss of air pressure forces an air conditioner to work harder to cool and ventilate your home, and leaks also can introduce unwanted dust and moisture into the air. Checking ductwork for leaks and properly sealing them is the first step to improving the efficiency of your system.

Mastic sealant
Paintbrush
Metal tape

Instructions

- 1
  Turn on the air conditioning fan. Start at the output duct located at the top of the air handling unit and feel for escaping air around all joints with your hand. Follow the ductwork through all accessible areas of your home and attic to identify as many problem areas as possible.
- 2
  Turn off the air conditioning fan and begin sealing. Where there are large leaks, use mastic sealant to repair the leak. Mastic sealant comes in liquid form and is applied with a paintbrush to duct joints. Allow the sealant to dry completely before turning on the air conditioning.
- 3
  Apply metal insulated tape to repair small leaks. Avoid using duct tape, which has a weaker adhesive and won't last as long as metal tape.

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