Duct Repair & Sealing

What duct repair and sealing actually is

Duct sealing closes the gaps in your ductwork so the air you paid to heat or cool reaches your rooms instead of the attic. Ducts leak at joints, at register boots, and wherever a run has sagged or pulled apart. ENERGY STAR says a typical house loses 20 to 30 percent of the air moving through its ducts to leaks, holes, and poor connections [1].

Repair is the mechanical part: reconnecting a run that fell off or replacing a crushed section of flex. A proper job then measures how much the system leaks, seals it with mastic and tape where hands can reach and aerosol where they can’t, and measures again. This is a different trade from duct cleaning. Cleaning takes dust out of ducts. It can’t close a gap.

What a proper duct sealing job looks like

1. A leakage test first. The tech covers the registers, pressurizes the system with a fan, and measures how much air escapes.
2. Finding the leaks. Reachable runs get a visual check; smoke or fog pushed through the system shows the rest.
3. Repairs before sealing. Disconnected runs get reconnected, crushed flex gets replaced, sagging sections get strapped.
4. Sealing the reachable runs by hand. Mastic, a thick paste, goes on joints and seams, foil tape where needed.
5. Sealing the buried runs from inside. For ducts in walls or under slabs, an aerosol sealant gets blown through the system and collects in the gaps. You’ll see a machine at the air handler and covered registers.
6. The test runs again and you see both numbers side by side. That before and after is what you’re paying for.

What it costs

Based on our 2025-2026 pricing research, whole-home duct sealing costs $1,000 to $6,000, roughly $1 to $2 per square foot of conditioned space. Aeroseal-style aerosol sealing usually lands between $1,300 and $3,000. A repair-only visit for a disconnected run or a few obvious leaks can be a few hundred dollars. Price tracks system size and how much of it is buried inside walls or a tight attic. This is one of the priciest jobs on this site and should only follow a leakage test. A bid with no measured leakage number is a guess with a dollar sign on it.

Do you actually need it?

You need it when the symptoms point at the ducts: a room or two that never reaches the thermostat setting, bills that keep climbing, ducts in an unconditioned attic or crawlspace, a run you can see hanging loose, or dust streaks at the edges of a register. Two or more together is a strong signal. Request quotes from providers near you, and ask each one to include a leakage test.

You can skip it if a leakage test comes back tight. A tight system with uneven rooms usually points away from the ducts, toward equipment or insulation. Try this first: check for a closed damper, a dirty filter, or a duct that’s fallen off in the attic, then get a standalone leakage test if you’re still unsure. If it shows real leakage, return here and request quotes.

How to choose a provider

• Ask whether the quote includes a leakage test before and after. If not, they can’t tell you what they fixed.
• Ask what they seal with. Mastic and foil tape for reachable joints, aerosol for buried runs. “Duct tape” as the main answer is a bad sign.
• Ask for before and after readings from a past job. A contractor who does this regularly has them.
• Get the scope in writing: which runs get hand-sealed, which get aerosol, what repairs are included, and the target leakage number.

Red flags: sealing sold during a cleaning visit with no test, a quote built on square footage alone, no repairs before sealing, and a promised dollar savings on your bill.

Sources

1. ENERGY STAR, “Duct Sealing,” Save at Home: Heating & Cooling. https://www.energystar.gov/saveathome/heating-cooling/duct-sealing