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

Sealing a leaking air duct improves HVAC efficiency by stopping conditioned air from escaping before it reaches your rooms. Most leaks occur at seams, boots, and around the air handler, and small gaps can add up to the airflow of an open register. For accessible, minor leaks, careful DIY sealing works; hidden runs, flexible ducts, or signs of moisture or mold call for a professional inspection and sealing. Technicians serving the Bellflower area often see leaks where metal trunks meet takeoffs and at floor or ceiling registers.

To address typical leaks, take these focused steps:

• Find leaks by feeling for air while the system runs and by spotting dust streaks at joints.
• Clean and dry metal; brush on water-based mastic across joints.
• For small gaps, apply UL 181 foil tape; never use cloth “duct tape.”
• Insulate sealed ducts in unconditioned spaces to limit energy loss. A duct leakage test after repairs confirms results and guides next steps. <br/>

Updated: 2026-04-01 <br/> Need help in Bellflower, IL? Call (309) 317-4215 or book online. “He suggested only two minor, optional items (UV bulb next spring and a small duct seal), both reasonably priced.” — Steve Whaley