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. For southern New Hampshire homeowners deciding between or replacing one of these, the choice usually comes down to what the home already has, what comfort feels right, and what the budget supports.
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 outside of the heat exchanger, picking up heat, and pushes the warm air through the home's ductwork to supply registers in each room. Return ducts pull room air back to the furnace, and the cycle repeats.
Key characteristics:
- Heats up and delivers warm air quickly
- Same ductwork can deliver cooling in summer (paired with central AC or a heat pump coil)
- Moves air, which can lift dust and dry the home in winter
- Filter and humidifier can be added to the system to address both issues
How a boiler works
A boiler burns gas, propane, or oil to heat water (not to boiling, just 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 the boiler to be reheated.
Key characteristics:
- Heats more slowly but delivers very even, comfortable warmth
- Easy to zone room by room (each zone has its own thermostat and circulator or valve)
- Quiet operation: no blower noise
- Does not move air, so does not lift dust or contribute to winter dryness
- Requires a separate system for cooling (typically central AC, ductless mini splits, or window units)
The naming confusion
Many NH homeowners refer to their boiler as a "furnace," and technically the older usage of the word "furnace" did include boilers. Plumbing and heating professionals today use the terms 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 supply registers in the walls or floor that blow warm air, you have a furnace.
Comfort differences
Furnace pros
- Fast recovery from a setback
- Same ducts deliver cooling in summer
- Easy to integrate filtration, humidification, and IAQ equipment
Furnace cons
- Air movement can feel drafty
- Dries indoor air in winter (humidifier helps)
- Ducts can leak or be poorly designed, creating uneven room temperatures
- Blower noise during operation
Boiler pros
- Very even, comfortable heat (especially with cast-iron radiators or radiant floors)
- Easy to zone
- Quiet, no blower noise
- No air movement, so no dust circulation
- Long equipment lifespan (cast iron: 25 to 30+ years)
Boiler cons
- Slower recovery from a setback
- Separate system needed for cooling
- More piping to deal with in a major retrofit
- Risk of frozen pipes if the system fails in extreme cold
When you can change types
Converting from one type to the other is a major project:
- Adding ducts to a boiler home requires running ductwork through walls and ceilings, which is invasive in finished space.
- Adding baseboards or radiators to a forced-air home requires 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 technically a third option that does not fit neatly into the furnace-or-boiler split. A heat pump 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 to either type of home through ductless mini splits
- 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. 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.