Abstract: The present invention discloses a method of compensating for a restricted intake in a two stage furnace. The furnace includes low and high pressure switches for determining if sufficient air is present to support low and high combustion. When the furnace operates at high combustion, the state of the high pressure switch is monitored to determine if the high pressure switch has changed state for a predetermined amount of time such as 15 seconds. The inducer fan is switched to low when insufficient air for high combustion has been indicated for such a predetermined time. If the state of the low pressure switch indicates that insufficient air is available for low combustion, then the inducer is turned on high.