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Insulation and Weatherization in NH

Updated 2026-10-10 · 5 min read

Air sealing before insulation, recommended R-values for NH, energy audits through NHSaves, income-based weatherization help, and attic hazards to check.

Seal the leaks first, then insulate

Air sealing and insulation do different jobs. Insulation slows heat moving through the walls and ceiling. Air sealing stops warm air from escaping through gaps around chimneys, plumbing and wiring holes, light fixtures, attic hatches, windows and doors. ENERGY STAR recommends sealing the attic first and adding insulation afterward (ENERGY STAR attic insulation). Leaks are easier to get at before new insulation covers them.

The EPA estimates that homeowners can save an average of 15% on heating and cooling costs by air sealing and adding insulation (ENERGY STAR). Your results depend on how leaky and under-insulated the house is to start with.

Some fixes are simple, like weatherstripping doors and caulking around windows. ENERGY STAR calls attic air sealing generally a challenging DIY project and suggests a contractor if you aren't comfortable doing it yourself (ENERGY STAR attic air sealing).

How much insulation for a New Hampshire home

Insulation is rated by R-value. Higher numbers resist heat flow better. ENERGY STAR publishes recommended R-values for existing homes by climate zone, based on the 2021 International Energy Conservation Code.

New Hampshire falls in climate zones 5 and 6. A U.S. Department of Energy county list places Cheshire, Hillsborough, Rockingham and Strafford counties in zone 5 and the other six counties in zone 6. ENERGY STAR gives zones 5 and 6 the same recommendations, so for retrofits the targets are the same statewide:

Attic with no insulation: R-60
Attic with 3 to 4 inches of existing insulation: add R-49
Floors: R-30
Basement or crawlspace walls: R-15 rigid insulation (sheathing) or R-19 batts
Walls: if the siding is coming off, ENERGY STAR suggests blowing insulation into empty wall cavities and adding R-5 to R-10 rigid insulation under the new siding. For 2x4 walls that are already insulated, it suggests adding R-10.

New construction and additions follow the energy code

The numbers above are recommendations for upgrading an existing home. New homes and additions have to meet the state energy code instead. According to the NH Division of Fire Safety, the code is the 2018 International Energy Conservation Code with New Hampshire amendments. Your town's building department can tell you what applies to your project. See our building permit guide.

Get an energy audit

An energy audit (also called an assessment) shows where your house is losing heat and which fixes are worth doing first. NHSaves, the energy efficiency program of Eversource, Liberty, the New Hampshire Electric Cooperative and Unitil, offers home energy audits, weatherization rebates and financing through its Home Energy Performance program.

NHSaves has a free online Home Heating Index tool that shows if your home qualifies for an audit. You'll need 12 months of heating fuel use, your conditioned square footage, your heating fuel, your utility and your zip code. Incentives and loan terms change, and they're offered while funding lasts, so check the NHSaves page for current details. Our energy rebate guide covers what's available now.

Free weatherization for income-eligible households

Two programs can cover weatherization costs for households that qualify by income:

The state Weatherization Assistance Program is run by the NH Department of Energy with federal grants and delivered by local Community Action Agencies. After you're found income eligible, you go on a waiting list. A certified energy auditor then does a home energy audit with diagnostic testing. Typical high-priority work includes attic air sealing, attic insulation, wall insulation where there is none, and air sealing or insulating basements and crawl spaces.
The NHSaves Home Energy Assistance program covers the full cost of weatherization and replacing inefficient equipment for income-eligible homeowners and renters.
For both, start by calling the Community Action Agency that serves your town. The NH Department of Energy says you can apply for electric, fuel and weatherization assistance at the same time.

Check the attic for hazards before work starts

ENERGY STAR recommends calling a professional before adding insulation if you find any of these (attic insulation project):

Vermiculite insulation: loose, pebbly fill that's usually gray-brown or silver-gold. The EPA says to assume vermiculite contains asbestos and leave it undisturbed. Don't store things in that attic, don't try to remove it yourself, and hire a professional asbestos contractor if remodeling would disturb it. See our asbestos guide.
Knob-and-tube wiring (pre-1930), which ENERGY STAR says can be a fire hazard in contact with insulation. Have a licensed electrician look at it first.
Wet or damp insulation (a sign of a roof leak), or moldy or rotted rafters or joists.
Kitchen, bath or dryer vents that blow moist air into the attic instead of outdoors.
Little or no attic ventilation.
Recessed can lights: ENERGY STAR says to keep insulation at least 3 inches away unless the fixture is rated IC (insulation contact), and never to lay insulation over soffit vents.
Metal flues: ENERGY STAR notes that building codes usually require 1 inch of clearance between metal flues and combustible material, including insulation.

Ventilation, moisture and combustion safety

A tighter house holds in moisture and indoor pollutants along with heat. ENERGY STAR warns that air sealing can cause naturally venting combustion appliances to back-draft exhaust gases into the home. It recommends having oil- and gas-fired appliances tested before and after air sealing, and says the house may need added mechanical ventilation (attic air sealing). A good weatherization contractor or energy auditor will check this as part of the job.

The NH Department of Energy also suggests running kitchen, bath and other ventilation fans for at least 20 minutes after cooking or bathing. Make sure you have working carbon monoxide alarms if you have any fuel-burning appliance. See our heating system guide for more on CO alarms.

Ice dams and windows

Heat leaking into the attic is the usual cause of ice dams in New Hampshire. Air sealing and insulation are the long-term fix, as explained in our ice dam guide.

For drafty windows and doors, ENERGY STAR notes that sealing behind the trim can pay off even if the windows themselves are airtight, and that windows and doors tend to be accessible areas suited to a do-it-yourself project. See its how-to for sealing behind window and door trim.

Hiring help

Get more than one quote, ask what air sealing is included, and ask what R-value the contractor will install in each area. Ask how they'll check combustion safety and ventilation when the work is done. Browse insulation contractors and window and door installers in our directory, and see our contractor hiring checklist.

This guide is general information. Program rules, funding and codes change, so confirm details with NHSaves, your Community Action Agency or your town's building department before you start.