Furnace Versus Boiler: What's the Difference?

While each is designed to heat your living space, they operate in very different ways. Furnaces achieve higher heating levels, but boilers use energy more efficiently and last longer.

Gas Furnace Operation

Furnaces heat air which a blower motor moves through a home's duct system. Traditional, forced hot-air, HVAC systems include an outdoor (air conditioning) and an indoor (furnace) unit. The furnace heats and circulates warm air in the winter. In the summer, it acts as a fan to blow cool air from the outdoor unit to cool your home.

Gas Boiler Operation

Boilers heat water which flows through a network of pipes connected to radiators in your home. Unlike gas furnaces, which offer little variation, boilers offer more variety, specifically in the way they vent exhaust. If you have a newer home, a boiler may make more sense.

Chimney-vented boilers exhaust through a chimney. Power and direct vent boilers push exhaust through roof or side wall vents with a fan. Power vent boilers only work in open rooms, not tight closets or crawl spaces. Condensing boilers require special venting because the exhaust they generate is acidic.

The method a boiler uses to vent its exhaust may determine the type of model you install:

• Condensing high-efficiency gas boiler (water only): Fueled by gas, these boilers achieve high efficiency by condensing water vapor in the exhaust gases.
• Atmospheric gas boiler: These boilers draw combustion air/fuel gases through the boiler with out a fan.
• High-efficiency gas, induced draft boiler (water only): A direct vent system that does not require a chimney because it vents byproducts through the house wall via metal or plastic vents.
• High-Efficiency gas, power-vented boiler (water only): These boilers use blowers or fans to exhaust gases by pushing them through horizontal vent pipes rather than a chimney or vertical vents.

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