Patent ID: 8672670

Claim:
A method of controlling a modulating gas furnace, comprising: monitoring a differential pressure associated with the modulating gas furnace using a low pressure limit switch configured to actuate at a first pressure, an intermediate pressure limit switch configured to actuate at a second pressure, and a high pressure limit switch configured to actuate at a third pressure, wherein the second pressure is between the first pressure and the third pressure; selectively operating the modulating gas furnace in one of a cycling mode, a modulating mode in a lower range, and a modulating mode in an upper range, the modulating mode in the lower range being associated with an output capacity range between the output capacity ranges of the cycling mode and the modulating mode in the upper range, wherein the modulating gas furnace is configured to selectively maintain steady state operation at a plurality of firing rates within at least one of the modulating mode in the lower range and the modulating mode in the upper range; and selectively operating the modulating gas furnace in response to at least one of the low pressure limit switch, the intermediate pressure limit switch, and the high pressure limit switch.