Why the drafts, dry winter air, ice dams and cold floors of a southern Maine house usually trace back to air leaks, where those leaks hide, how they are sealed safely, and what Efficiency Maine pays for sealing each zone.
Efficiency Maine says the air leaks in a poorly sealed house can add up to the equivalent of an open window. Where the Jetport logs 6,795 heating degree days in a normal year, that window stays open through a long season.
Air sealing is usually the cheapest work on an insulation job and the part that does the most. It is also the part nobody sees once the insulation is in, which is why it gets skipped. This page covers what leaks do to a house here, where they hide, the materials that suit each spot, the safety side of a tighter house, how the results are measured, and Efficiency Maine's three air sealing rebates.
Efficiency Maine describes the path: cold air comes in through gaps low in the house, picks up heat, and leaves through the upper floor and the attic. The list of problems it ties to that loop reads like a southern Maine winter:
Its air sealing page adds two signs most people miss: musty smells drifting up from the basement, and spider webs, which tend to collect where air moves in basements and crawl spaces.
Windows and doors get the blame, and Efficiency Maine's myths sheet says that is mostly wrong: the biggest leaks are hidden from view, passing through floors and ceilings and around chimneys, pipes and ductwork. Its air sealing page names the usual suspects around the chimney, at plumbing penetrations and at recessed lights.
In practice the work concentrates at the top and the bottom of the house, where the pressure pushing air through is strongest:
Doors and windows still get weather stripping where they need it, and Efficiency Maine pays a small rebate for that living-space work.
No single product seals a house. Efficiency Maine lists the materials its registered vendors use, caulk, spray foam, metal flashing, weather stripping and rigid foam, and notes that some suit particular spots better than others.
| Where | Usual material |
|---|---|
| Wire and pipe holes, top plates | Canned foam or caulk |
| Large openings, dropped soffits, chase tops | Rigid foam board, sealed at the edges |
| Around a chimney or flue | Metal flashing and fire-rated caulk |
| Rim joist and sill | Closed-cell foam, or board sealed in each bay |
| Attic hatch, doors | Weather stripping, with insulation on the hatch |
The chimney row is the one that matters most for safety. Efficiency Maine names fire-rated caulk and metal flashing for high-temperature spots such as the chimney, and its checklist keeps anything combustible apart from chimneys and flues, and from light fixtures not rated to be covered.
A tighter house keeps more of what is inside it, moisture included. Efficiency Maine's air sealing page lists two cautions: moisture problems should be fixed before or as part of the sealing, and in extreme cases a house can be made tight enough to need a ventilation system or make-up air for the heating system, which is why the work is done with blower door testing.
Its myths sheet answers the old line that a house has to breathe: houses need fresh air, but most have far more leaks than they need, and air that comes in through basements, garages and crawl spaces brings their air with it. Controlled ventilation is better than accidental leaks.
For rebated jobs the checklist turns that into steps: fans that vent into the attic or basement are taken outdoors, mechanical ventilation is recommended where it is needed, a carbon monoxide detector has to be in the living space where there is a fuel-burning appliance or attached garage, and open-flue appliances are tested for spillage once the sealing is done.
Air sealing is the one part of the job that can be measured before and after. A blower door depressurizes the house and records how much air leaks in, in cubic feet per minute at 50 pascals; a thermal camera or smoke pencil shows where. Efficiency Maine's claim form records both numbers on a rebated job, and the vendor runs the tests unless a safety issue, a wood or pellet stove in use, or repairs under way prevent it.
New homes have a stricter target. Maine's energy chapter changed the air-leakage limit a new house must test at from the national code's 5.0 to 3.0, measured as air changes per hour at that same test pressure. An older house is not held to that number, but the before-and-after test shows how much of the gap the sealing closed. The energy assessment page explains the test in more detail.
Without the test, the only evidence is photographs of each sealed spot, which we take either way.
Efficiency Maine pays for air sealing separately from insulation, once per zone. Under the table that took over on October 1, 2026, with the work done by a vendor on its registered list:
Those sit alongside the insulation rebates for the same zones and count toward the same lifetime limit of $8,600 per home. The low and moderate tiers need the household verified before the claim; the space has to be heated through the season. The energy code and rebate guide has the insulation table as well.
Air sealing usually costs least of anything on an insulation proposal, and it comes first in the order of work, so it is rarely worth skipping even where the rebate is small.
Yes, and it comes first. Efficiency Maine likens insulation with no sealing to a knit sweater with no shell over it: the fiber slows heat, but only sealing stops the air carrying it away.
Most houses leak far more than they need. A blower door test shows how tight the house gets, and where it becomes very tight, mechanical ventilation is the better way to bring in fresh air.
Efficiency Maine's view is that air leakage is the most common cause: cold outside air that leaks in loses relative humidity as it is heated. Sealing the leaks can help more than running a humidifier.
No. Efficiency Maine names metal flashing and fire-rated caulk for hot spots such as chimneys, and its checklist keeps flammable materials away from chimneys and flues.
Per zone: $150 to $300 for the attic, $100 to $200 for the basement or underbelly, and $50 to $100 for the living space, depending on income tier, on work by one of its Residential Registered Vendors.
Air sealing across greater Portland and southern Maine, from the Casco Bay islands to the York County coast and the Sebago Lake towns. Each city has its own page with the permit rule and code edition that apply there:
Sources: Leaks as an open window; cold air enters low; drafts, dry air, frozen pipes, ice dams · Where leaks are; materials; chimneys; musty smells and spider webs; moisture and ventilation · Hidden leaks; houses do not need to breathe through leaks; dryness · Flammable materials, fans, ventilation, CO detector, spillage test, blower door · Air sealing rebates by zone and tier; lifetime limit · Pre- and post-upgrade CFM50 on the claim form · Maine's air-leakage change for new homes · Portland Jetport heating degree days. Codes, programs and prices change; confirm the current rule with your city before you rely on it.
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