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Furnaces & Boiler Systems
Most homes are heated with either furnaces or boilers. Furnaces heat air and distribute the heated air through the house using ducts. Boilers heat water, and provide either hot water or steam for heating. Steam is distributed via pipes to steam radiators, and hot water can be distributed via baseboard radiators or radiant floor systems, or can heat air via a coil. Steam boilers operate at a higher temperature than hot water boilers, and are inherently less efficient, but high-efficiency versions of all types of furnaces and boilers are currently available.
A central furnace or boiler’s efficiency is measured by annual fuel utilization efficiency (AFUE). AFUE is a measure of how efficient the appliance is in converting the energy in its fuel to heat over the course of a typical year. An AFUE of 90% means that 90% of the energy in the fuel becomes heat for the home and the other 10% escapes up the chimney and elsewhere. An all-electric furnace or boiler has no flue loss through a chimney. The AFUE rating for an all-electric furnace or boiler is between 95% and 100%.
High-efficiency heating systems:
- Condensing flue gases in a second heat exchanger for extra efficiency
- Sealed combustion
- 90% to 98.5% AFUE
How Does a Boiler Work
- Boilers heat water.
- The water is turned into steam or hot water.
- Steam heat moves through pipes into the rest of the house and is dispersed through radiators. Hot water versions move water through baseboard radiators or radiant floor systems, or they heat air via a coil.
- Boilers run on various energy sources, including natural gas, oil, electricity, and wood.
How Does a Furnace Work?
- Furnaces heat air.
- The heat is distributed by a blower through your home’s duct system. The hot air is released into the room through registers or vents in the floors, walls or ceilings.
- Also known as hot air heating systems, furnaces can run on electricity, natural gas, propane, or oil.
- Furnaces are more common in newer homes because they generally cost less than boilers. There are, however, pros and cons to each.
- Boilers usually use less fuel to heat your home.
- More consistent heat.
- Boilers are generally quieter than furnaces.
- Less maintenance: Boilers do not have filters that require cleaning.
- Better air quality: Since boilers don’t blow air, they don’t spread dust or allergens.
- Slower to react: Boilers take longer to adjust to thermostat changes.
- Harder to install: Boilers are more difficult to install than furnaces.
- Harder to convert: Switching from a boiler heating system to one run by a furnace is almost impossible.
- Leaks pose a hazard: If your boiler leaks water, your home can sustain serious water damage.
- Less expensive: Since furnaces are more common than boilers, they are less expensive.
- Reduced leak hazard: Furnaces that leak usually only leak air, which is clearly less able to do damage to your home than a boiler filled with water.
- No freezing hazard: Since furnaces do not contain water, the system is not in jeopardy of freezing if the power goes out.
- Easier to install: Furnace installation typically takes a few hours, as compared to days in some boiler installations.
- Less efficient: Heating with air is less efficient than heating with water. That means that your furnace will use fuel more quickly than a boiler.
- More noise: Furnaces blow air and that makes the sound.
- Reduced heat consistency: Forced air heat is not as consistent as steam or hot water heat. As a result, some rooms may be cooler or hotter than others.
- Inferior air quality: Since furnaces blow hot air, they also blow dust and allergens.