If you are replacing a heating system, buying an older house, or planning an addition, you may be choosing between a boiler and a furnace. Both can keep a Minnesota home warm through a long heating season. They work in different ways, and that difference affects comfort, cooling options, air quality and what a replacement involves.
How each system heats your home
A furnace burns gas (or uses electric elements) to heat air. A blower pushes that air through supply ducts to registers in each room, and return ducts bring air back to the furnace.
A boiler heats water. The U.S. Department of Energy describes hydronic systems as ones that use steam or hot water heated by a boiler and distributed to radiators, convectors or radiant floors. You can read this in the Department of Energy HVAC guide for homeowners. Most newer boilers circulate hot water with a pump. Many older St. Paul homes still have steam boilers with cast iron radiators.
Comfort differences you will notice
The two systems feel different in daily use:
- Even heat. Radiators, baseboard and radiant floors warm surfaces and people in the room. Many homeowners find boiler heat steadier, with fewer warm and cool swings.
- Noise. A boiler has no blower pushing air through registers. You may hear pipes tick as they warm up or a pump running, but there is less air noise.
- Air movement. A furnace moves air, which spreads heat quickly after a thermostat change. A boiler system usually takes longer to bring a cold room up to temperature.
- Drafts and dust. Forced air can stir up dust. Hot-water heat does not move air through the house, so there is no duct system to collect dust.
- Floor and wall space. Radiators and baseboard take up wall space. Furnace systems need room for ducts and registers instead.
Efficiency and operating costs
Both furnaces and boilers are rated by annual fuel utilization efficiency (AFUE), which measures how much of the fuel becomes heat over a typical year. A higher AFUE means less fuel wasted.
The highest-efficiency gas furnaces and boilers are condensing models. They recover extra heat from the water vapor in the exhaust. The Department of Energy also notes that steam boilers operate at higher temperatures than hot-water boilers and are inherently less efficient. If your home has steam heat, that matters when you compare long-term fuel use.
Your actual heating bill depends on several factors:
- The AFUE of the equipment you choose
- Whether the system is sized from a room-by-room heat loss calculation
- The condition of your ducts or your radiators and piping
- Insulation and air sealing in the house
- How well the controls are set up, including outdoor reset on a boiler
For Minnesota winters, the Department of Energy guidance on residential gas boilers is direct: in a cold climate with significant heating needs, it usually makes sense to invest in a highest-efficiency system. See our guide to high-efficiency boiler installation for more on condensing models.
Air conditioning, humidity and air quality
This is often the deciding factor. A furnace shares its ducts and blower with central air conditioning. It can also carry a whole-house humidifier and a media air filter, which help with dry indoor air during sub-zero stretches.
A boiler home has no ducts, so central AC is not built in. Your options include:
- Window or portable units
- Ductless mini-split heat pumps, which mount on the wall and need only a small line set through the exterior wall
- Adding a separate duct system, usually in an attic or closets
If your summers are humid and you want whole-home cooling, factor that cost and work into the decision. Many boiler owners choose ductless mini-splits for cooling and keep the boiler for heat.
Switching from one system to the other
Most homeowners replace like with like. Switching is possible, but it is a larger project.
- Boiler to furnace: You need ductwork run to every room. In a finished older home, that can mean opening walls and ceilings, and the radiators and piping usually come out.
- Furnace to boiler: You need piping and heat emitters (baseboard, radiators or radiant tubing) in every room. You still keep or need ducts if you want central AC.
- Steam to hot water: Some steam radiators can be reused with hot water, but steam piping often has to be modified or replaced. A technician must evaluate this.
Steps you can take before you get quotes
You can gather useful information on your own:
- Find out what you have now. A boiler connects to pipes, not ducts. A steam boiler has a sight glass that shows the water level. A hot-water boiler has a pressure and temperature gauge.
- Read the rating plate on your current equipment and write down the model and serial number.
- List rooms that run too cold or too warm in winter, and note which rooms are hard to cool in summer.
- Decide how much cooling you want. Whole-home AC changes the comparison.
- Confirm you have working carbon monoxide alarms. Minnesota Statutes section 299F.51 requires one within 10 feet of each room used for sleeping.
Do not open burner panels or adjust gas controls yourself. If you smell gas, leave the house right away, do not use switches or phones inside, and call 911 and your gas utility from outside.
When to call a professional
Call a heating contractor when your current boiler or furnace needs a major repair, when one or more rooms will not stay warm, or when you are planning a remodel that adds or removes living space. A technician should do a heat loss calculation and look at your existing distribution system before recommending either option. Krinkie's installs and services both systems. You can compare details on our boiler service page or call 651-488-5555 to schedule an in-home evaluation.
Common questions
Is a boiler more efficient than a furnace?
Not by default. Both are rated by AFUE, and high-efficiency condensing models exist for each. Steam boilers are inherently less efficient than hot-water boilers, according to the U.S. Department of Energy.
Can I add central air conditioning to a house with a boiler?
Yes, but a boiler home has no ducts, so you need either a new duct system or ductless mini-splits. Mini-splits are often the simpler option in a finished home.
Can I switch from a boiler to a furnace?
Yes, but you must add ductwork to every room, and the radiators or baseboard usually come out. A contractor should evaluate the house before you decide.