How to Seal Ductwork Leaks

The ductwork in your home supplies conditioned air to each room of your house. When you have leaks in your ductwork, the airflow is reduced throughout your home, costing you money. If the return ductwork of your HVAC system leaks, contaminated air pulls into the duct system from your attic or basement. This causes the air quality of your home to deteriorate and can cause problems with your family's health. Using a mastic duct sealer to seal the leaks in your ductwork will ensure that your ductwork will remain leak free for many years.

Things You'll Need

• Droplight
• Extension cord
• Fan
• 2-inch-wide metal scraper
• Clean rags
• 2-inch-wide paintbrush
• Water-based mastic sealer
• Roll of fiberglass mesh-tape
• Scissors

Instructions

1. Turn off the HVAC unit to stop air from flowing through the ductwork.

2. Plug in the droplight and the extension cord and run them to the area where you will be sealing your ductwork.

3. Direct the fan to blow the air from the area, plug in the fan and make sure that the air flowing from the fan is unobstructed.

4. Inspect the longitudinal seams of the ductwork and the connections between the pieces of ductwork for missing duct sealer or duct tape.

5. Scrape the loose duct sealer from the ductwork with the 2-inch-wide metal scraper. If your duct seams are sealed with duct tape, remove all the duct tape from the ductwork. Duct tape breaks down over time and is not adequate for sealing ductwork seams.

6. Wipe the area around the longitudinal seams and duct connections with clean rags to remove dust and debris from the areas you will apply mastic.

7. Load the 2-inch-wide paintbrush with water-based mastic sealer and run the paintbrush along the duct seams and connections. Reload the brush often to avoid thin spots developing in the mastic.

8. Pull a length of fiberglass mesh from the roll and cut it with the scissors.

9. Press the fiberglass mesh into the wet mastic when the gaps you are sealing exceed 1/4 inch in width.

10. Run the paintbrush loaded with mastic over the fiberglass method to embed the mesh into the mastic.

11. Allow the mastic to cure and then re-inspect the duct connections to ensure that the mastic did not shrink and pull away from the surface of the ductwork.

Tips & Warnings

• Wear a chemical respirator if you are using solvent-based mastic sealer in place of water-based mastic to protect yourself from the fumes emitted from the mastic.

References

• Duct Sealing: Energy Star
• Arizona Public Service Company: Reducing Duct Leakage
• Duct Materials: Mastic