Boiler vs Furnace: Which Heating System Is Better? (2026 Comparison)

A furnace heats air and blows it through ducts; a boiler heats water and circulates it to radiators, baseboards or floor tubing. Both burn the same fuels and are rated the same way, so the choice is less about cost and more about comfort, ducts and cooling.

On the same fuel and efficiency, a boiler and a furnace cost about the same to run: heating a 2,000 sq ft home with average insulation takes about 58 million BTU a year, roughly $829 with either at 95% efficiency and an assumed $1.35 per therm. Boilers give quiet, even radiant heat without ducts; furnaces share ducts with central air.

How they heat

• Furnace (forced air): burns fuel to heat air, which a blower pushes through supply ducts; return ducts bring it back.
• Boiler (hydronic): heats water, which a pump circulates through radiators, baseboard convectors or tubing in the floor, then back to the boiler. Steam boilers, common in older buildings, send steam instead.

Side-by-side comparison

Most of the choice comes down to how each one moves heat and whether it shares hardware with cooling. This table lines up the factors that differ; efficiency and running cost get their own sections below.

Steam vs. hot-water boilers

Boilers come in two kinds, and older homes often have the steam type. A hot-water boiler keeps the water well below boiling and uses a small electric pump, called a circulator, to push it through radiators or baseboard and back.

A steam boiler instead boils the water. At sea level water turns to steam at 212°F, so the steam rises through the pipes on its own pressure, gives up its heat at the radiator, condenses back to water, and drains to the boiler by gravity.

Because steam runs hotter and cannot easily throttle up and down, steam systems respond slowly and generally run less efficiently than hot-water ones. Condensing efficiency needs low return-water temperatures, so condensing boilers are hot-water models, not steam.

Efficiency and federal minimums

Both are rated by AFUE, the share of fuel that becomes heat over a year. Gas furnaces must meet 80% AFUE today, and non-weatherized gas furnaces made from December 18, 2028 must reach 95%.

Gas-fired hot-water boilers must meet 84% AFUE. Condensing models of both reach 90% and above, the efficiency that defines a condensing unit; condensing boilers are most efficient with low water temperatures, such as radiant floors.

Running cost

Heat delivered is what costs money, so at the same efficiency and fuel price the bills match. For the example home's 58 million BTU a year at an assumed $1.35 per therm:

See the heating cost calculator for other fuels.

Comfort

Boilers heat by radiation and gentle convection, so rooms feel even, with no drafts or blowing dust; they're also quieter. Furnaces heat faster and can filter and humidify the air through the ducts. Radiant floors, in particular, keep floors warm; see radiant floor heating pros and cons.

Cooling and ductwork

A furnace's ducts also serve central air, so one duct system does both. A boiler has no ducts, so cooling needs a separate system, often ductless mini splits. Adding ducts to a boiler-heated house is usually a major job.

Retrofit reality

Switching how heat is distributed is the expensive part, not the appliance itself. Going from a boiler to a furnace means adding a full duct network through finished walls and ceilings; going the other way means running water pipes and placing radiators or floor tubing.

Changing fuel, such as oil to gas, adds its own work: a new gas line, meter and venting. Because these jobs vary so much by house, get itemized local quotes rather than a rule-of-thumb number.

Which fits your home

• Boiler: you already have one, want radiant comfort, or are building with radiant floors; plan separate cooling.
• Furnace: you have ducts or want central air, want filtration, or want faster heat-up.
• Neither: a heat pump heats and cools without combustion; see furnace vs. heat pump.

Picking by your situation

• Old home with radiators or baseboard already: keep hydronic and replace like for like with a boiler, which avoids tearing out walls for ducts; a condensing model pays off most if your radiators can run at lower water temperatures.
• New build or gut renovation: either works, so let cooling decide; central air from one duct system favors a furnace, while radiant-floor comfort points to a boiler with separate cooling.
• Planning to add air conditioning later: a furnace already gives you the ducts central AC needs, whereas a boiler home will most likely add ductless mini splits instead.

Frequently asked questions

Is a boiler more efficient than a furnace?

Not inherently. Both are rated by AFUE, and condensing models of each reach 90% and above, the efficiency that defines a condensing unit. On the same fuel and AFUE, they cost the same to run.

Which is cheaper to run, a boiler or a furnace?

At equal efficiency and fuel price, about the same. In the example home, a 95% model of either costs about $829 a year at an assumed $1.35 per therm.

Can I switch from a boiler to a furnace?

Yes, but it means installing ductwork, which is usually the largest part of the cost. Ductless heat pumps are a common alternative.

Do boilers provide air conditioning?

No. A boiler only heats; cooling needs a separate system such as mini splits or central air with ducts.

Can I add central air conditioning to a boiler-heated house?

Yes. Because a boiler has no ducts, the usual options are ductless mini splits, which need no ductwork, or a separate central AC system with its own air handler and new ducts. Mini splits are common here because they avoid cutting duct runs into a finished house.

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