Comparison
Difference between a boiler and a furnace
Both burn fuel or use electricity to make heat. They move that heat through the house in different ways.
Written by HYRE HVAC Research Desk Primary-source research, data analysis and fact checking
The short answer
The difference between a boiler and a furnace is what they heat. A furnace heats air and a blower pushes it through ducts to vents.
A boiler heats water, and a pump circulates it through pipes to radiators, baseboards or floor tubing. Furnaces share ducts with central air conditioning; boilers need a separate way to cool. Both are rated by AFUE for fuel efficiency.
How does a furnace work?
A furnace burns natural gas, propane or oil in a burner, or uses electric elements. The heat passes through a sealed heat exchanger, and the blower motor pushes house air across the outside of it.
Warm air travels through supply ducts to each room and returns through return ducts. Combustion gases leave through a flue or vent and never mix with the house air when the heat exchanger is intact.
Because the furnace already has a blower and ducts, it usually houses the indoor coil for central air. One duct system serves both heating and cooling.
How does a boiler work?
A boiler heats water in a sealed vessel. A circulator pump sends hot water through pipes to radiators, baseboard convectors or tubing in the floor.
The water cools as it gives up heat and returns to the boiler. Older systems may use steam rather than hot water.
There are no ducts, so the heat moves through the house without blowing air.
Many boilers also heat domestic hot water through an indirect tank or a built-in coil. Combi boilers do both in one unit.
Boiler vs furnace at a glance
| Furnace | Boiler | |
|---|---|---|
| Heats | Air | Water or steam |
| Delivers heat through | Ducts and vents | Pipes to radiators, baseboard or floors |
| Shares with AC | Yes, same ducts and blower | No; needs separate cooling |
| Feel | Fast warm-up, moving air | Slower, even radiant heat, quiet |
| Filtration | Central filter cleans house air | None; no air movement |
| Efficiency rating | AFUE | AFUE |
| Typical faults | Ignitor, flame sensor, blower, limit switch | Pressure, leaks, circulator pump, air in lines |
Why do homes have one and not the other?
Mostly history and region. Older homes in cold northern climates were often built with boilers and radiators.
Homes built later, and most homes in warmer regions, use furnaces and ducts because the same ducts carry air conditioning.
Switching between them is a large job: adding ducts to a boiler house, or removing pipes from a furnace house.
What drives the cost of each?
Replacing like with like is the normal case. For a furnace, cost turns on size, efficiency tier, venting and how the AC coil fits.
For a boiler, it turns on size, venting, the near-boiler piping and whether the unit also makes hot water. We publish no prices here: we do not yet hold enough sourced, dated quotes to state one honestly.
Use the cost hub and the HVAC cost calculator with your own quotes.
Safety notes for both
Leave the house and call the gas utility or 911 from outside. Do not touch switches or the thermostat.
Any fuel-burning furnace or boiler can produce carbon monoxide if something goes wrong. CPSC advises alarms on every level and outside sleeping areas.
ENERGY STAR’s checklist includes gas connections, gas pressure, burner combustion and the heat exchanger. That is contractor work.
Pressure relief valves protect the vessel. If the gauge runs high or the relief valve drips, call a licensed technician.
Which one is better?
A furnace is better when
You want central air through the same ducts.
You want whole-house air filtration.
You want fast warm-up after a setback.
A boiler is better when
You value quiet, even radiant heat with no drafts.
The house already has a sound hydronic system.
You want one appliance to heat the house and the water.
Questions
Is a boiler or furnace more efficient?
Does a boiler need ducts?
Can I have AC with a boiler?
Which lasts longer, a boiler or furnace?
How do I know which one I have?
Written and audited by
HYRE HVAC Research Desk
Primary-source research, data analysis and fact checking
We are a research desk, not a sales floor. We read the federal microdata file, the statute or the manufacturer data sheet ourselves, and we publish the figure with the document it came from and the date we retrieved it.
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