Furnace vs Boiler in NH Homes

Updated 2026-09-30

Furnaces and boilers both heat New Hampshire houses. They do not heat them the same way, and the house you bought often chose for you decades ago. A furnace heats air and pushes it through ducts. A boiler heats water or makes steam and sends it to radiators, baseboard, or tubing in the floor. If you are deciding whether to repair, replace, or add a heat pump, you need to know which machine you have. An independent contractor can confirm it on a visit. Call (603) 420-0791 with your ZIP code. Confirm license and insurance. This site does not prefer one appliance over the other and does not set the price.

How to tell them apart without a manual

A furnace is a box with a blower, a filter rack, and sheet-metal ducts leaving the top or the side. Supply registers are in the floors, walls, or ceilings. The same ducts often carry central air in the summer. A boiler is a smaller appliance, often cast iron or a wall-hung condensing unit, with pipes, circulators or zone valves, and an expansion tank or, on steam, a sight glass and different vents. Radiators or baseboard sit along the walls. Some houses have both: a boiler for the original rooms and a ducted furnace or a ductless head for an addition. Do not assume the thermostat on the first floor controls everything.

Fuels

Both appliances may be natural gas, propane, or oil. Gas mains are not statewide. The Public Utilities Commission describes two regulated gas utilities: Liberty (EnergyNorth) and Northern Utilities, a Unitil company. Liberty's own community list includes Manchester, Nashua, Concord, and many Merrimack Valley towns, and it also lists Laconia, with a note that a few towns including Derry have only a very small gas area. Northern's service is the seacoast and southeastern New Hampshire, which is why Portsmouth and Dover conversations often start with gas even in older houses. If your street has no main, the realistic fuels are oil, propane, or a heat pump. A contractor who quotes a gas furnace on a street without gas is quoting a utility extension you may not get.

Electric furnaces exist and are expensive to run. Electric baseboard is not a boiler. Say what you actually have when you call.

Comfort and the building

Forced air can filter and can add central cooling. It also moves dust, and it fails in rooms where the ducts never went. Hot water is quiet and suits houses that were never ducted, including a lot of pre-war housing and capes. It does not filter air and it does not cool. Adding central air to a boiler house means ducts, a high-velocity system, or ductless heads. That is a different project from replacing the boiler. Steam, where it still exists, wants a contractor who still works on steam. Bleeding a hot-water baseboard and venting a steam radiator are not the same task.

Replacement paths

A failed furnace can be replaced with another furnace, or the heating can move to a ducted heat pump if the ducts and the electrical service can take it. A failed boiler can be replaced with another boiler, or the house can move to ductless heat pumps if you accept the look of the heads and a backup plan. Mixing the two without a plan leaves you with an orphaned chimney, a water heater that lost its vent, or rooms with no heat. Read when to repair or replace and heat pumps in winter.

What the contractor should check

Fuel, venting, the condition of the heat exchanger or boiler sections, the size relative to the house, and what the water heater is doing. Ask for a load conversation, not a like-for-like swap of a unit that was always short-cycling. Permits are local. Licensing for gas work is the fuel gas fitter credential described in how to vet a contractor. Oil certification at the state board is voluntary. Ask anyway.

Service pages: furnace repair, furnace replacement, boiler repair, and boiler replacement. The price is quoted after a visit. People in photos are actors or models. This site does not warrant the work.

Additions and the system you already have

The most common hybrid in this state is an old boiler house with a ductless head or a small furnace added onto an addition. The thermostat in the living room does not know about the addition. When you call for "no heat," say which system is quiet. Replacing the boiler will not fix a failed mini-split, and replacing the mini-split will not fix a boiler zone valve. Label the thermostats. It sounds trivial and it saves a service call.

If you are choosing a single system for a renovation, decide whether you want filtration and cooling. That choice pushes you toward ducts or ductless heads. If you want to keep radiators, you are keeping a boiler or you are planning a different heat source room by room. There is no wrong answer that fits every house. There is a wrong answer that ignores the house you have. Walk it with the contractor and point at the cold room before they sell the appliance.

If you are buying a house, look at the mechanical room before you look at the countertops. The fuel, the vent, the age of the heat exchanger or the boiler sections, and the presence or absence of ducts decide your first-year budget more than the paint color. Ask the seller for service records. Absence of records is not a defect by itself. It does mean your first call after closing should be a tune-up, not a shocked no-heat night in February. Call (603) 420-0791 with the ZIP code once you own the house or once you have permission to have it looked at. Do not schedule work on a house you do not have authority to open.

When you call, use the right noun. Say furnace if you have ducts and a blower. Say boiler if you have pipes and radiators or baseboard. Say both if you have both. That one word changes who should take the job and what parts they bring. It also stops a referral from turning into a wasted trip. The ZIP code still decides coverage. The fuel still decides the license you should verify. Those three facts, said clearly, are the useful start of the call.

Furnace vs boiler in New Hampshire homes