Air duct sealing & insulation
Ductwork running through an unconditioned attic, crawl space or garage loses twice: through the metal, and out of every joint it was never properly sealed at. Serving New Jersey and Pennsylvania.
Duct in an unconditioned attic loses heat two ways. Some conducts straight through the duct wall into a space that’s below freezing in January and above 130°F in July. The rest simply escapes — out of joints, boots, and connections that were taped once with something that gave up years ago.
Insulation only addresses the first one. Leakage is usually the larger number, and it’s the part people don’t see, because a leaking duct looks identical to a working one from the outside.
Which is why the order matters: seal first, insulate second. Wrapping insulation around a leaking duct hides the problem and makes it harder to find later.
Not the furnace, not the thermostat, not the insulation in the ceiling.
Work on the ductwork itself, leaving the attic or crawl space as it is.
Right when: the attic stays vented, the duct run is accessible, and the budget is focused.
Insulate the roof deck so the attic becomes conditioned. The ducts are then inside the house, and the problem stops existing.
Right when: your air handler is in the attic, or you were considering attic work anyway. See attic insulation.
If your air handler and most of your ductwork live in the attic, the second option is usually the one worth pricing. It costs more up front and it fixes the cause rather than managing the symptom.
Foam over ducts we haven’t sealed. Once foam is applied, that joint is behind a permanent layer. If it was leaking when we covered it, it’s leaking forever and nobody will ever find it. Sealing is not an upsell here — it’s the prerequisite.
Bury damaged duct. Crushed flex, a boot that’s pulled off its collar, a run that sags into a U and collects condensate. Insulation doesn’t fix any of that, and encapsulating it makes the eventual repair a demolition job. If we find it, we tell you, and it gets repaired first — by us or by your HVAC contractor.
Encapsulate a system that needs replacing. If the ductwork is at the end of its life, or undersized for the equipment, foam is money spent on something that’s coming out. We’d rather you heard that from us before the invoice than from an HVAC tech after it.
We’re an insulation contractor, not an HVAC company. Where the right answer is duct repair, redesign or replacement, we say so and stay in our lane.
Cold supply air runs through a metal duct. That duct sits in an attic at 130°F and high humidity. The duct surface drops below the dew point of the air around it, and water forms on the outside of it — the same way it forms on a glass of iced tea.
Then it drips. Onto the insulation below, onto the ceiling drywall, onto whatever is stored up there. People usually call a roofer about the stain first.
Insulating the duct to a proper thickness keeps the outer surface warm enough that condensation can’t form. Conditioning the attic removes the humid air entirely. Both work — but doing neither means a slow moisture problem in your ceiling that gets blamed on the roof every summer.
Why there’s no simple square-foot price here: duct jobs vary enormously. A short accessible run in a basement is a couple of hours. A tangle of flex in a low attic with the air handler buried at the far end is a different job entirely, and quoting it from a phone call would be guesswork.
If you’re weighing this against attic insulation, get both priced in one visit. The comparison is usually clearer than people expect, and often the attic wins on value. Other pricing is on the main pricing section.
Get a written priceSeal first, every time. Leakage is normally the larger loss and it’s the one insulation does nothing about — conditioned air escaping into an attic is gone regardless of how well wrapped the duct is. Once the system is tight, insulation stops what’s left from conducting away. Doing it in the other order means paying to hide the bigger problem.
Only after it’s been sealed and inspected, and only where the ductwork is sound. Foam creates a permanent layer — anything wrong underneath becomes invisible and expensive to reach. We look at the condition of every accessible run before we agree to encapsulate anything, and on plenty of houses our recommendation is to insulate the attic instead and leave the ducts alone entirely.
Then that gets fixed before anything else, and it’s more common than you’d think — a boot knocked off its collar by someone storing boxes, flex duct crushed under a walkway board, a run sagging into a low spot. None of it is an insulation problem. We’ll photograph what we find so you can see it, and either your HVAC contractor handles it or we coordinate with them.
Yes, and it’s one of the clearer wins. Condensation forms because the duct surface drops below the dew point of the humid attic air around it. Insulating to a proper thickness keeps that surface warm enough that water can’t form. Conditioning the attic removes the humid air altogether. Either approach stops the dripping, which also stops the ceiling stains people usually blame on the roof.
Much less. A basement is closer to indoor temperature than an attic ever gets, so conduction losses are small and leakage stays broadly inside the house. Sealing joints is still worthwhile for balance and airflow, but insulating basement ducts is rarely the best use of the money. If your basement is unheated and uninsulated, the better project is the foundation walls — that fixes the ducts as a side effect.
Physically relocating ductwork in an existing house is disruptive and expensive, and it’s rarely worth it on its own. The practical version of the same idea is to move the boundary rather than the ducts — insulate the roof deck so the attic becomes conditioned, and the ducts end up inside the house without anyone touching them. For a home with the air handler in the attic, that’s usually the strongest option on the table.
Requirements depend on where the duct runs and which code edition your jurisdiction enforces, and they’re higher for ducts outside the conditioned envelope than for those inside it. Ducts already inside the heated space generally need little or none. We confirm the applicable requirement for your township at the assessment rather than quoting a number from memory — and if the thickness needed is impractical in a low attic, that itself is an argument for conditioning the space instead.
Tell us which part of the building is the problem. We’ll come out, measure, and give you a written fixed price. No obligation to proceed.
