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Sound Comparison

How long do furnaces operate at High and Low firing rates? Of course, it depends upon many factors including your climate area, the outside temperature, the amount of insulation in your home, the thermostat setpoint, and how large of a furnace you have compared to the heating needs of your home, which is often referred to as "oversize."

The width of the sound level bar provides an approximation of the percentage of operating time that the furnace operates at this sound level during the heating season, again based upon a national average—the wider the bar, the more the furnace operates at that sound level. As stated before, the actual time spent at the various firing rates will vary based on a number of factors, throughout the heating season and from home to home.

Based on a national average, two-stage furnaces split their time of operation between their lowest and highest firing rates; with approximately 90% of their operating time at the lowest rate and approximately 10% at the highest rate. These furnaces will provide longer, more comfortable heating cycles than their single-stage counterparts.

Modulating furnaces will spend approximately 80% of the heating season operating at their lowest firing rate, based on a national average, and approximately 1% at their highest firing rate, with the remaining operation somewhere between low and high fire. Since these furnaces are able to modulate down to under 50% of their full firing rates, they will operate longer than other furnaces, provide more even heating, and usually provide the best comfort.


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