HVAC tune-ups and duct sealing
Leaky ducts waste 20–30% of what your system produces. Sealing them rides the same 75–90% weatherization rebate as insulation, and it is the cheapest comfort fix in the house.
The least glamorous money on the site
Nobody is excited about duct sealing. It is also, dollar for dollar, one of the highest-return things you can do to a forced-air house — and it is one of the few measures that improves comfort in both seasons at once.
Typical duct systems lose 20–30% of the air they move through leaks at joints, boots and plenums. When those ducts run through an unconditioned attic, crawlspace or cellar — which is where most of them run in Upper Valley houses — that air is heating the outdoors in January and dumping cool air into a crawlspace in July. You paid to condition it either way.
How the rebates treat this
Duct sealing is generally treated as a weatherization measure rather than an equipment purchase, which is good news: it rides on the same percentage-based incentives as insulation and air sealing.
| New Hampshire | Vermont | |
|---|---|---|
| Duct sealing | Folded into weatherization at 75% of cost | Folded into weatherization at up to 90% cash back |
| Duct insulation | Same weatherization treatment | Same weatherization treatment |
| Assessment that identifies it | $100 copay Home Performance assessment | Required assessment gates the rebate |
| Annual equipment tune-up | Not directly rebated; protects rebate-required efficiency | Not directly rebated; protects rebate-required efficiency |
Because duct work is scoped inside a weatherization project, it must generally be done by the same participating or Efficiency Excellence Network contractor doing the rest of the envelope work.
What proper duct sealing involves
- Diagnosis first. A duct blaster pressurizes the system and measures actual leakage, so you know what you started with and what you fixed.
- Mastic, not duct tape. Fabric duct tape fails within a few years in an attic or cellar. Brush-applied mastic and mesh at joints, boots and plenum seams is the durable repair.
- Boot sealing at the floor and ceiling. Where the boot meets the subfloor or drywall is a major and commonly ignored leak.
- Insulation on ducts in unconditioned space. Sealing stops the leak; insulation stops the conduction. Both matter in an unheated attic.
- Balancing. Once the leaks are gone, airflow to distant rooms changes — dampers usually need adjusting.
Annual tune-ups, and why they protect your rebate
Rebate programs pay for rated efficiency. A heat pump with a fouled outdoor coil, a dirty filter and a low refrigerant charge does not deliver rated efficiency, which means you are paying to run a system you were subsidized to install and getting less than either you or the program assumed.
A yearly service visit on a heat pump or air conditioner should cover:
- Refrigerant charge verified against the manufacturer’s spec — not topped up on a hunch
- Indoor and outdoor coils cleaned
- Filters replaced or washed; blower wheel checked
- Condensate drain cleared, which is what stops the ceiling stain
- Electrical connections, contactors and capacitors checked
- Defrost cycle operation confirmed — important here, largely irrelevant further south
On an oil or propane boiler or furnace, annual service also means combustion analysis, nozzle and filter replacement and a flue check. That is a safety item as much as an efficiency one.
Change your filters. A clogged filter is the most common cause of a system that “stopped working properly,” it raises energy use immediately, and in a wood-heated house it happens faster than the label on the box suggests. Check monthly through the heating season.
What it costs
- Duct sealing, typical house: $1,200–$3,000 before rebate
- Duct insulation in an unconditioned attic: $800–$2,200
- Annual heat pump or AC tune-up: $150–$300
- Annual boiler or furnace service: $200–$400
Scoped inside a Vermont weatherization project at up to 90% cash back, a $2,000 duct sealing job can come back to roughly $200. That is not a typographical error, and it is why it is worth asking your auditor to include the ducts in the scope rather than treating them as a separate job later.
What to ask for
Ask for the before-and-after duct leakage numbers in writing. A contractor who measures is a contractor who can prove the work; a contractor who does not measure is guessing, and so are you.
Figures checked July 2026. Rebate programs change their amounts, caps and equipment requirements during the year, and several are capped by available funding. Confirm the current offer with the program or your contractor before you sign anything.
HVAC tune-up & duct sealing: common questions
Is duct sealing rebated separately?
Usually not — it is scoped inside a weatherization project and rides the same percentage incentive: 75% in New Hampshire, up to 90% in Vermont. The practical consequence is that you should have the ducts included in the audit scope from the beginning rather than treating them as a separate job afterwards.
How much heat am I actually losing through leaky ducts?
Twenty to thirty percent is the widely used range for an unsealed system, and it is worse when the ducts run through an unconditioned attic or crawlspace — which describes most Upper Valley duct systems. A duct blaster test gives you your actual number rather than an average.
Can I just use duct tape?
No, despite the name. Fabric duct tape dries out and lets go within a few years in the temperature swings of a Vermont attic. The durable repair is brush-applied mastic with mesh reinforcement at joints and seams, plus properly sealed boots.
How often should I service a heat pump?
Annually, ideally before the heating season. Clean coils, correct refrigerant charge and clear condensate drains are what keep the system delivering the efficiency the rebate was calculated on. Filters need checking far more often than that — monthly in a wood-heated house.
My upstairs is always colder than downstairs. Is that a duct problem?
Often partly, yes — leakage and poor balancing send conditioned air where you did not intend it. But in an Upper Valley house it is just as likely to be the attic plane and the stack effect pulling warm air out of the top of the house. An audit with a blower door distinguishes the two, which is why it is worth doing before you spend money on either.
Get the ducts into the audit scope
Scoped inside a weatherization project, duct sealing carries the same 75–90% rebate as insulation. We’ll make sure it is included.