To seal a leaking air duct and improve HVAC efficiency, use HVAC-rated foil tape or duct mastic on clean, dry seams and replace any torn sections that won’t hold a seal. Most leaks form at joints and transitions where metal meets flex duct, especially around the air handler and supply boots.
- Turn off the system, locate leaks by feeling for air or using a smoke pencil, and mark them.
- Clean the metal, remove old cloth tape, and dry the area fully.
- Apply duct mastic with fiberglass mesh on gaps or use UL-listed foil tape; press firmly and cover the full seam.
- Support sagging flex, seal boots to the ceiling or wall, and recheck airflow after 15 minutes. We frequently repair leaky ducts in coastal Pinellas homes, where attic heat and salt air can loosen older joints. If you see mold, wet insulation, or damaged flex, stop work and schedule a professional inspection.
Updated: 2026-04-01
Need help in Tierra Verde, FL? Call (727) 416-2314 or book online. “Jesse and his associate arrived on time and completed all of the duct cleaning and equipment cleaning as scheduled.” — Robert P.