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

You can seal a leaking air duct by cleaning the joint and applying HVAC mastic or UL 181 foil tape to all gaps and seams to cut air loss and improve efficiency. Most leaks come from loose connections at boots, elbows, and flex-duct collars, which leak conditioned air into attics or crawlspaces. Small, reachable leaks are a reasonable DIY fix; widespread leaks, crushed ducts, or signs of moisture or contaminants call for a pro. We provide professional duct sealing using the industry’s best sealing materials to boost comfort and reduce dust, and we often see these leaks in Central Texas homes we service.

Try these simple steps:

• Turn off the HVAC and expose the leaking joint.
• Wipe dust away so sealant adheres.
• Brush on mastic or apply UL 181 foil tape; avoid cloth “duct tape.”
• Seal around boots, takeoffs, and flex connections.
• Recheck airflow after it cures.

If ducts are hard to access or damage is present, schedule a professional inspection before running the system. <br/> Updated: 2026-04-01 <br/> Need help in Bastrop, TX? Call (512) 309-0360 or book online. "Anthony came by and gave us a quote for dryer vent/duct cleaning." — Lali M.