I know what the difference is. Are there any opinions about the necessity for either. I've had one estimate with what I think is a single stage Rheem furnace. I think it's single stage because the contractor never mentioned it being two stage. I've had another estimate with a competing brand for a two stage furnace. My two stage estimate is more costly understandably. How much of a difference price difference should one expect going from a single to a two stage furnace?