How to Seal Rigid Aluminum Duct

Seams on rigid aluminum elbows allow air to leak from a duct system.

Air leaks around the connections and seams of installed rigid aluminum duct decreases the efficiency of a duct system. This increases wear on the equipment moving air through the system and increases the costs associated with running air through the rigid aluminum duct. Unlike high-pressure duct systems that require strong mastic sealers to seal the duct, rigid aluminum systems require a minimal amount of sealant to stop leaks. Although numerous types of sealants exist, one type applies with no mess and matches the finish of installed aluminum duct.

Things You'll Need

• Marker
• Clean rags
• Aluminum foil tape
• Utility knife

Instructions

1. Turn off all equipment sending or pulling air through the rigid aluminum duct. Allow the duct to depressurize for 5 to 10 minutes.

2. Mark all areas on the duct that have dirt lines - clear signs of a leak - with a marker. Wipe debris from each connection and seam of the installed rigid aluminum duct with a clean rag. Use multiple rags to ensure all areas are free of contaminants.

3. Pull the paper backing away from the end of a piece of aluminum foil tape until 2 inches of adhesive - located on back of the tape - are exposed. Hold the exposed end of foil tape 1 inch above a connection or 1 inch past the start of a seam. Push the foil tape forcefully against the duct to hold it in place.

4. Pull the paper backing away from the secured end of foil tape. Push the tape against the duct as the adhesive is exposed. Cut the foil tape when the secured section sits at least 1 inch past the end of the seam, connection or leak with a utility knife.

5. Fold the piece of paper - removed from the back of the tape - in half two times. Rub the folded section of paper from the tape to remove any air bubbles sitting between the foil tape and the rigid aluminum duct. Move along the duct marking, cleaning and sealing each component.

6. Turn on the equipment to pressurize the system after all the aluminum foil tape has been placed on the seams, connections and leaks.

Tips & Warnings

• Wear leather gloves to protect your hands from cuts from aluminum foil tape.

References

• "Low Income Advisory Board"; Duct Sealing Standards
• "Berry Plastics"; HVAC Tapes
• "3M"; Aluminum Foil Tape 1450 Technical Data Sheet