Short answer
It depends on the home. NH law (RSA 153:10-a) requires fire warning devices and carbon monoxide detectors in every rental unit and multi-unit dwelling, and in single-family homes built or substantially rehabilitated after January 1, 2010. A CO detector isn't required if the unit has no attached garage and no fuel-burning appliance. Local rules can be stricter, and FHA 203(k) renovation loans require a smoke detector by each sleeping area.
Single-family homes
Under RSA 153:10-a, a single-family home built or substantially rehabilitated after January 1, 2010 must have automatic fire warning devices and carbon monoxide detectors. The CO requirement doesn't apply if the home has no attached garage and no combustion appliance, such as an oil, gas or propane furnace, boiler, water heater or stove. If one is added later, a CO detector is required. For older homes, check with your town's fire department, since local rules can be stricter than state law.
Even when the law doesn't require them, working alarms are cheap and worth checking at your inspection and final walk-through. See do you need a home inspection.
Buying a 2-4 unit home or a home with a rental unit
The same law requires every multi-unit dwelling and rental unit to have fire warning devices and, with the same exception, carbon monoxide detectors. Once you own the building, you're responsible for keeping the devices in working order in the units you rent. That includes an accessory dwelling unit you rent out. See buying a multi-family home in NH and ADUs and in-law apartments.
Does my mortgage require alarms?
For most purchase loans, the appraiser checks that the home is safe and meets the loan's property standards, and local code applies. Renovation loans are more specific: HUD's Handbook 4000.1 says an FHA 203(k) work write-up must include at least one listed smoke detector next to each sleeping area. Battery-powered detectors are allowed in existing buildings, but new additions need detectors wired to the building's power, following local code. See renovation loans in NH.
Quick checklist
- Ask the seller or listing agent whether alarms were part of any recent renovation or permit.
- Test the alarms at the final walk-through.
- If you're buying a home with tenants, confirm each unit has working devices before closing. See buying an NH home with tenants.
- Call your local fire department with questions about what applies to your home.
Sources
- NH RSA 153:10-a, Fire warning and carbon monoxide devices
- HUD Single Family Housing Policy Handbook 4000.1, Update 18 (August 2026), 203(k) Consultant Requirements
Checked November 2, 2026. Rules and dates change, so confirm current details before you rely on them.
General information only, not tax or legal advice. Program availability, eligibility and terms vary by lender and are subject to change and to underwriting approval. Not a commitment to lend.