Difference Between a Boiler and a Furnace

The price of energy rises with each passing year. It’s important to know where your money is going when it comes to heating your home. Whether you are making a decision on a heating system for a new home, considering a switch, or just curious, we’re answering the questions “what does a boiler do?” and “what’s the difference between a boiler and a furnace?” The short answer is “hot water vs hot air,” but we will dig into this deeper. In addition, we’ll talk about the pros and cons of each system in regard to cost, efficiency, and effectiveness.

What Does a Boiler Do?

A boiler does exactly what the name implies–boil water! Water is boiled in a hot water tank, then distributed via pipes as hot water or steam to radiators or baseboard heaters in rooms throughout a house. Boilers are radiant heat systems, heating pipes that in turn heat the air around them (radiate heat).

Most boilers use natural gas, electricity, or oil, but boilers using alternative fuels including wood, corn pellets, and other renewable energy sources are available. In gas boilers, the water in the hot water tank is heated using jets. In electric boilers, heating elements in the hot water tank bring water to the appropriate temperature.

Boilers are known for their efficiency–they are closed-loop systems. The water that goes out to heat the house returns to the hot water tank to be heated again. Since the water is already fairly hot, it takes little heat to bring it back to a boil. Boilers are hydronic heating systems, meaning they transfer heat by circulating water.

What’s the Difference Between a Boiler and a Furnace?

Whereas a boiler heats a home via the circulation of hot water, a furnace heats a home via the circulation of hot air. Air is heated then distributed throughout a house using ductwork and vents. This is called forced-air heating.

Furnaces can be fueled by natural gas or electricity just like boilers, but propane is also common. Oil, geothermal and solar-powered systems are rare, alternative options. Electric furnaces are heated using coils. A current is run through the coils until they are red hot and heat the air around them. Natural gas furnaces burn gas to create hot combustion gas which enters a metal heat exchanger, heating the air around it.

Furnaces can heat a house quickly and to high temperatures. Boilers take longer to warm up but are known to be more efficient and longer lasting. Furnaces require air filter replacement on a monthly to quarterly bases. They require more frequent repairs than boilers, which can go longer without maintenance. At the same time, boilers need to be bled for excess air periodically, and owning a boiler means risking frozen pipes–something that owning a furnace does not risk. When it comes to air quality, however, boilers take the stage. The ductwork that furnaces require can accumulate dust and dirt that mixes with the air. Boilers do not use ductwork and humidify the air as a byproduct of their hydronic system.

Both boilers and furnaces come with a unique list of pros and cons. Having a better idea of what they do and how they are different from each other can put confidence in decisions about heating and home energy as prices rise. A good rule of thumb is to remember that boilers use hot water, and furnaces use hot air.