Furnace vs Boiler: Which Home Heating System Is Better?

A furnace heats air and blows it through ducts. A boiler heats water and sends it through pipes to radiators, baseboards or tubing in the floor. On the same fuel at the same efficiency rating, the two cost the same per unit of heat. So the choice usually comes down to your house: keep a furnace if you have ducts and want central air on the same system, and keep a boiler if the house is already piped for hot water.

How a furnace and a boiler heat your home

Both burn a fuel (or use electricity) to make heat. The difference is what carries that heat to your rooms. The U.S. Department of Energy (DOE) explains it in its Energy Saver Guide:

• Furnace: a central forced-air furnace sends heated air through the house via ducts. Most run on natural gas; others use electricity, oil or propane.
• Boiler: heats water, either as hot water or steam, and sends it through pipes to upright radiators, baseboard convectors or radiant floor tubing.

The same DOE guide calls furnaces the most common way to heat a home in the United States. This page compares a gas furnace with a hot-water (hydronic) boiler, the two you are most likely choosing between. Steam boilers exist too, and the federal rules rate them separately.

If you are also weighing an electric option, our heat pump vs furnace comparison covers that side.

Efficiency: AFUE ratings and the federal minimums

Furnaces and boilers share one efficiency rating, AFUE (Annual Fuel Utilization Efficiency). ENERGY STAR describes it in its furnace product criteria as the share of the heat in the fuel that becomes space heat instead of being lost. An 80% AFUE furnace turns 80% of the gas it burns into heat for your home.

The federal minimums sit in 10 CFR 430.32, the Code of Federal Regulations section on appliance standards:

• Non-weatherized (indoor) gas furnaces: 80%, rising to 95% for furnaces made on and after December 18, 2028.
• Non-weatherized oil furnaces: 83%.
• Gas hot-water boilers made on and after January 15, 2021: 84%. Oil hot-water boilers: 86%.
• Steam boilers: 82% for gas and 85% for oil.

ENERGY STAR sets the bar higher. A certified gas furnace needs at least 95% AFUE in the southern US and 97% in the northern US, and an oil furnace 87%. Its boiler page asks for 90% on gas boilers and 87% on oil boilers.

So on paper a minimum boiler beats a minimum furnace (84% against 80%), but the best gas furnaces are rated higher than the ENERGY STAR level for gas boilers. Compare the AFUE of the actual models you are quoted, not the type of system. The DOE guide says to look for the ENERGY STAR and EnergyGuide labels when you buy.

What each one costs to run

We use the same formula as our heating cost by fuel calculator: price per unit ÷ (Btu per unit × AFUE) × 1,000,000. That gives the cost of one million Btu (British thermal units) of heat delivered to your home.

The prices are U.S. Energy Information Administration (EIA) residential averages: natural gas at $15.34 per thousand cubic feet (2025 average) and heating oil at $6.233 per gallon (week of October 26, 2026, before taxes). Heat content comes from the EIA's Btu conversion factors: 1,036 Btu per cubic foot of gas and 138,500 per gallon of heating oil.

Two things stand out. The fuel matters far more than the system: oil heat costs over three times as much as gas at these prices, whether a furnace or a boiler burns it. And within one fuel, the gap is only the AFUE gap. Prices change, and your state's may be very different, so run your own numbers in the calculator. Our guide to the cheapest ways to heat your home ranks every fuel, including propane and heat pumps.

Lennox and Trane both say on their furnace vs boiler pages that it takes less fuel to heat water than air. We found no government figure that measures this, and AFUE rates only the appliance, not the ducts or pipes. What the DOE guide does put a number on is ducts: ducts that leak into an attic or crawl space can add hundreds of dollars a year to heating and cooling bills, and sealing and insulating them is usually very cost effective.

Cooling, air filtration and humidity

This is where a furnace pulls ahead for many homes. The DOE guide says your ducts carry the air from the furnace and the central air conditioner to each room. One set of ducts and one blower serve both. Carrier's 59SC5A furnace installation manual shows how: the air conditioner's cooling coil goes on the downstream side of the furnace. Trane adds that the furnace then moves the cooled air in summer as well as the heated air in winter.

A boiler cannot cool. Trane says so plainly on its furnace vs boiler page. If you want air conditioning in a boiler home, you add a separate system. The DOE guide points to ductless mini-split heat pumps, which install without ducts and can cool (and heat) individual rooms.

A furnace also filters the air it moves. The Carrier manual says never to run the furnace without a filter or filtration device in place, and allows an accessory air cleaner in place of the filter rack. A boiler moves no air, so it has no filter. Lennox's furnace vs boiler guide counts that as a plus for the boiler, since there is no filter to clean.

Dry winter air affects both. Carrier's furnace humidifier guide says cold air holds less moisture, which leaves indoor air dry in winter. With a furnace you can add a whole-home humidifier to the ductwork, and Carrier suggests keeping indoor humidity between 30% and 50%. A boiler home has no ducts to carry one, so you would use a room humidifier instead.

Noise and comfort

A furnace blower makes noise as it pushes air into the ducts, Lennox says, and it calls boilers quieter. Trane sees it a little differently: a boiler system can be noisier than a furnace as the pipes and radiators heat up.

One boiler noise has a known cause. Weil-McLain's gas boiler user manual lists radiators or baseboards that stay cold or are noisy, and puts it down to air in the system. The fix is to bleed the air out through the vents on the radiators or baseboards. Our guide on how to bleed a baseboard heater walks through it.

Lennox says heat from water or steam is more consistent than forced air, and that with a furnace some rooms are more comfortable than others. We have not measured that ourselves, so treat it as the maker's view.

Maintenance: what the manuals ask of you

Both need a yearly visit from a technician. What differs is what you do between visits. Here is what two makers' manuals list for owners.

Gas furnace (Carrier 59SC5A). Check and clean the air filter each month, or more often if needed, and replace it if torn. Check the blower each heating and cooling season, and inspect the burner area and vent pipe before each heating season. A qualified service person should inspect the furnace once a year.

Gas boiler (Weil-McLain CGa Series 4 and sister models). A qualified technician must inspect and start the boiler at the beginning of every heating season. Between visits the manual lists daily checks of the boiler area, air openings and pressure gauge, and monthly checks of the piping, venting, air vents and relief valve. It also asks for a low water cutoff test every 3 months and a relief valve test every 6 months, and for the boiler water chemistry to be checked at least once a year.

Steps vary by model, so follow the manual for your own unit. On safety, the Weil-McLain manual says that if you smell gas, do not light any appliance or touch electrical switches, and call your gas supplier from a phone outside the building. It also requires at least one carbon monoxide alarm in the living space before the boiler runs.

If your furnace will not start, our checklist for a furnace that won't turn on covers the checks you can make before you call.

How long each one lasts

The makers do not agree, so here are their figures side by side. Trane says a well-maintained furnace lasts 15 to 20 years and a boiler with maintenance up to 30. Lennox gives gas furnaces 20 to 25 years and boilers 10 to 25 years, depending on type, use and maintenance.

The DOE guide gives one rule for both: consider replacing a furnace or boiler that is more than 15 years old, especially if it needs frequent repairs or your bills are rising. Our guide to how long a furnace lasts covers the warning signs.

Which one fits your house

The pipes or ducts you already have usually decide this. Trane says it is most cost-effective to keep the system you have rather than convert to the other. Swapping a boiler for a furnace means installing ductwork at the same time, and Trane notes you may also need an electrical upgrade. Lennox adds that older homes are more often boiler homes and new houses usually have furnaces.

Both can heat zones separately:

• Furnace: Carrier's zoning system guide describes motorized dampers in the ductwork, a zone control panel and a thermostat in each zone. Carrier says many existing systems can be retrofitted.
• Boiler: Weil-McLain's CGa boiler manual shows zoning with a circulator pump per zone or with zone valves.

Installed prices vary with your house, your region and the work involved. We have no government source for them, so we do not quote any. Both Trane and Lennox say a boiler usually costs more to install than a furnace because the job is more complex. A local quote that includes a heat-load calculation is the only figure worth comparing.

Who should pick which

Pick a furnace if your house has ducts, if you want central air conditioning on the same system, or if you want a filter and a whole-home humidifier built into the air flow. A model at 95% AFUE or more gives the lowest running cost on gas in the table above.

Pick a boiler if your house already has radiators, baseboards or radiant floor tubing, and you do not want air blown around the house. Look for 90% AFUE or more on gas, plan separately for cooling, and budget time for the owner checks in the manual.

If neither system is in the house yet, compare the full quotes, and ask a local HVAC technician to size the system to your home.