How Can I Seal a Leaking Air Duct to Improve HVAC Efficiency?

To seal a leaking air duct for better HVAC efficiency, use mastic sealant or UL 181-rated foil tape on accessible joints and seams, not cloth duct tape. Most leaks come from loose connections, failed old tape, or gaps where ducts meet vents and the air handler. DIY sealing works for visible, reachable spots; widespread or hidden leaks usually need a technician who can pressure-test, seal, and verify airflow. Lanz Plumbing, Heating & Cooling, Inc. also offers ductwork repair and can pair sealing with duct cleaning using our high‑power vacuum truck for a cleaner system, and we service homes in and around Alvin.

Try these focused steps:

• Run the fan to find leaks by feel or incense, then switch power off.
• Wipe dust, then brush on mastic; embed mesh over larger gaps.
• Seal register boots to drywall with mastic or UL 181 tape.
• Insulate bare ducts in unconditioned spaces after sealing.

If you notice rust, crushed flex, or suspected asbestos wrap, pause work and call a professional.

Updated: 2026-03-30

Need help in Alvin, IL? Call 217-247-4108 or book online.