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Sound Comparison

The sound levels of the furnaces tested vary from the level of a whisper, around 40 dBA during the lowest firing rates, up to 60 dBA, or the sound level of conversation, during the highest firing rates.

The height of the bar indicates the relative sound level, measured in decibels, produced by the furnaces tested in the mode selected - either the lowest or the highest firing rate of the furnace.

The minimum level of the bars is the normal ambient sound level of a room, or approximately 35 dBA. The maximum level is 70 dBA, or a bit above the highest level measured of any of the furnaces tested. Compare the height of the bars to compare the measured sound levels. In some cases, the bars will be similar heights, but the furnaces may sound quite different, perhaps with the furnace with the shorter bar sounding louder to your ear.

Based on the volume level during the playback on your computer, some recordings may be difficult to hear. The "Start Up" and "Low Fire" sequences can be especially quiet.

What do we mean by Low and High fire? Furnaces are grouped into three categories those that have three or more firing rates, also called "modulating" furnaces, dual firing rate furnaces, also known as two-stage furnaces, and single firing rate furnaces, also known as single-stage furnaces. Modulating and two-stage furnaces have their lowest and highest firing rates compared. The single-stage furnaces are only compared at high fire.

The low fire rates of the modulating furnaces tested are 35% to 40% of the full capacity of the furnace, while the low fire rates of the two-stage furnaces tested are 65% to 70% of the full capacity of the furnace. The low fire rates of each modulating and two-stage gas furnace tested are shown as a percentage of their full gas input rate. The high fire rate recordings for modulating and two-stage furnaces are done at their full gas input. Single-stage furnaces are operated and compared at their full gas input capacity.

We chose to test furnaces from a variety of manufacturers that have high fire input gas rates of 65 to 85 thousand BTUs per hour. This range represents some of the highest sales volume of furnaces sold in North America.

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