Duct Sealing and Insulation: Stop Paying to Heat Your Attic

TL;DR: Leaky ducts can waste 20–30% of the air your system moves. Sealing and insulating them is one of the best efficiency upgrades.

_Last reviewed: July 2026 · 2 min read_

Leaky ducts can waste a large share of the heated and cooled air your system produces — air that escapes into the attic or crawlspace instead of your rooms. Sealing and insulating them is one of the highest-return efficiency upgrades there is. Four steps: find the leaks, seal them right, insulate the runs, and balance the airflow.

How do I find duct leaks?

Feel along the duct joints with the system running — escaping air is easy to detect with your hand (a little smoke from an incense stick makes it obvious). Focus on the seams, connections, and where ducts meet registers and the air handler. Accessible ducts in the basement, attic, and crawlspace are where the leaks (and the fix) usually are.

What should I seal ducts with?

Use mastic (or foil tape), not cloth "duct tape." Despite the name, regular duct tape dries out and falls off ducts within a year or two. Brush duct mastic over the joints and seams (or use UL-listed foil tape), which stays sealed for the long haul. Seal every accessible joint you found leaking.

Why insulate ducts?

Ducts running through unconditioned spaces — attics, crawlspaces, garages — lose heat through their walls even when sealed. Wrap those runs in duct insulation so the air arrives at the room temperature you paid for. Sealing stops air escaping; insulation stops heat escaping. Together they're a big efficiency win, part of a broader energy-saving plan.

How do I check that rooms get even airflow?

Compare airflow at each room's vent with the system running. A room that's always too hot or cold, or has weak airflow, points to a leak, a blockage, or a balancing issue in that branch. Noticeably uneven airflow is also one of the HVAC warning signs worth chasing down.

Track the work and savings

Logging which ducts you sealed and insulated lets you watch the payoff on your bills. Okoniq Property Hub keeps it with your utility bills and home maintenance records in one private place.

Frequently asked questions

How much can duct sealing save?

The U.S. Department of Energy estimates sealing and insulating ducts can recover a significant share of lost conditioned air — meaningful savings, especially with ducts in unconditioned spaces.

Should I hire a pro for duct sealing?

Accessible joints you can seal with mastic yourself. For ducts buried in walls or a whole-system "Aeroseal"-type job, an HVAC pro with the right equipment is the way to go.

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FAQ

How long does duct mastic last compared to regular duct tape?

Duct mastic and UL-listed foil tape stay sealed for decades, while regular cloth duct tape dries out and falls off within a year or two.

Can I seal ducts in my crawlspace myself or do I need a professional?

You can seal accessible ducts in crawlspaces and attics yourself with mastic or foil tape; hire a pro only for ducts buried in walls or whole-system Aeroseal treatments.

What type of insulation should I wrap around ducts in my attic?

Wrap ducts in unconditioned spaces like attics with duct insulation designed for HVAC — it stops heat loss through the duct walls even after the joints are sealed.

Will sealing ducts fix uneven heating between rooms?

Sealing leaks helps, but uneven airflow may also point to a blockage or balancing issue in that branch, so check airflow at each vent with the system running.