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Single-Stage Versus Two-Stage Furnaces – What’s the Difference?

posted by: Bart Manning

Two is definitely better than one when you’re talking about a two-stage furnace. The burner in a conventional single-stage furnace has just two outputs: zero percent and 100 percent. The furnace is either completely idle and providing no heat to your home—or it’s running full blast. Sort of like stop-and-go city driving, efficiency suffers and fuel expenses increase.

The fact is, once a house has been heated up, 100-percent burner output isn’t usually required simply to maintain the thermostat setting. A two-stage furnace is designed to sense the difference in the home’s heating load and automatically make the adjustment to a lower output of around 65 percent. Here are some reasons that make a second stage a good investment when upgrading to a new furnace:

  • Lower energy expense. Running at 25 to 35 percent less output most of the time means proportionately less energy is consumed and operating costs decline accordingly.
  • More consistent heating. In between the off and on cycles of a single-stage furnace, temperatures in living spaces often drop noticeably, up to 10 degrees off the thermostat setting. Air circulation also ceases, allowing rising warm air in rooms to accumulate at the ceiling, where it contributes little to the comfort level in the room. Because a two-stage furnace runs longer at lower output, temperature swings between on and off cycles average only about two to three degrees. More sustained air circulation also prevents stratification of hot air at the ceiling and warms rooms more evenly.
  • Quieter operation. The roaring of full burner output is noisy and that sound transmits through ducts into rooms. Reduced output in the second stage is quieter, particularly in smaller living quarters.
  • Improved air quality. Adequate filtration depends on air circulation through the system air filter. When a single-stage furnace cycles off, circulation also ceases and filtration stops. A two-stage furnace runs longer on cycles at lower output, sustaining filtration for longer periods and improving air quality.

For more information about the benefits of a two-stage furnace, contact us at Air Treatment, Inc.

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