How do furnaces and boilers differ?
The short answer: a furnace heats air and circulates it through ducts. A boiler heats water and circulates it through pipes to baseboards, radiators, or radiant floor tubing. Different fluid, different distribution, different equipment.
At A.J. LeBlanc Heating, we install and service both across NH. Here is how they actually compare.
How a furnace works
A furnace burns gas, propane, or oil to heat a metal heat exchanger. A blower pushes air across the heat exchanger and sends the warm air through the home's ductwork to supply registers in each room. Return ducts pull room air back, and the cycle repeats. It heats up and delivers warm air quickly.
How a boiler works
A boiler burns gas, propane, or oil to heat water, not to boiling but to roughly 140 to 180°F. A circulator pump moves the hot water through supply pipes to baseboards, radiators, or radiant tubing. The water gives up heat to each room and returns to be reheated. It heats more slowly but delivers very even, comfortable warmth.
The naming confusion
Many NH homeowners call their boiler a "furnace," and the older usage of the word did include boilers. Today the terms are used more strictly:
- Furnace: forced hot air system that heats air
- Boiler: hydronic system that heats water
If you have baseboards, radiators, or radiant floors, you have a boiler. If you have registers that blow warm air, you have a furnace.
Comfort trade-offs
A furnace recovers fast from a setback, makes it easy to add filtration, humidification, and other IAQ equipment, and the same ductwork can deliver cooling in summer when paired with central AC or a heat pump coil. The downsides: air movement can feel drafty and stir dust, it dries indoor air in winter, ducts can leak or run unevenly, and the blower is audible.
A boiler gives very even, comfortable heat, especially with cast-iron radiators or radiant floors. It zones easily room by room, runs silently with no blower noise, and circulates no dust, so it does not add to winter dryness. Cast-iron units last 25 to 30+ years. The downsides: slower recovery from a setback, more piping in a retrofit, a risk of frozen pipes if the system fails in extreme cold, and a separate cooling system, typically central AC, ductless mini splits, or window units.
When you can change types
Converting from one type to the other is a major project. Adding ducts to a boiler home means running ductwork through walls and ceilings, which is invasive in finished space. Adding baseboards or radiators to a forced-air home means running piping and installing emitters in every room.
For most NH homeowners, replacement-in-kind (boiler for boiler, furnace for furnace) is the practical choice. The exception: adding ductless mini splits to a boiler home is straightforward and adds both cooling and supplemental heat without changing the existing system.
What about heat pumps?
A heat pump is a third option that does not fit neatly into the furnace-or-boiler split. It can replace a furnace and use the existing ductwork (a "central heat pump"), replace a boiler and use existing baseboards (less common; "air-to-water" heat pumps), add zoned heating and cooling through ductless mini splits, or pair with an existing furnace or boiler as a dual-fuel system.
Schedule a consultation
If you are deciding what to do with an aging furnace or boiler, contact A.J. LeBlanc Heating or call 603-623-0412. We will walk through your options based on what your NH home already has and what you want for the next 20+ years. Serving New Hampshire families since 1928.
Frequently Asked Questions
Is a boiler the same thing as a furnace?
No. A furnace heats air. A boiler heats water. Different equipment, different distribution.
Which is more efficient, a furnace or a boiler?
Both can reach AFUE ratings of 95+ percent. Real-world efficiency depends on how well the equipment is matched to the home's distribution system. A condensing boiler paired with high-temperature baseboards may never reach its condensing range; a properly sized condensing furnace usually hits its rated efficiency.
Which lasts longer?
Cast-iron boilers typically last 25 to 30+ years. Gas furnaces typically last 15 to 20 years. Condensing boilers typically last 15 to 20 years.
Can I have both?
Many NH homes do. The boiler provides hydronic heat to the main living areas while a separate forced-air system (or ductless mini splits) provides cooling and supplemental heat to specific rooms.
Is forced air or hydronic heat better for allergies?
Hydronic does not circulate air, so it does not stir up dust or allergens. Forced air can be excellent for allergies if the system uses a high-MERV filter or media filtration, which provides ongoing air cleaning the hydronic system cannot.