How it works
Dual fuel puts a heat pump outside and keeps a gas furnace inside, on the same ducts and one thermostat. The heat pump replaces your air conditioner, so summers feel the same. In winter it pulls heat out of the outdoor air.
Above the temperature you set, the heat pump heats the house. Below it, the furnace takes over. Set it at 25°F and the furnace runs about 880 hours of an average Denver winter, roughly five weeks spread across the season. See other settings on the winter chart.
What changes in the basement
The coil on top of the furnace is replaced with one that heats as well as cools. New refrigerant lines run from it to the outdoor unit, and a new thermostat with an outdoor sensor runs both. A furnace in good shape can stay, though plenty of people replace it at the same time.
Why keep gas
The furnace covers cold snaps. If the heat pump needs a repair in January, you switch the thermostat to the furnace and the house stays warm. When the heat pump defrosts its outdoor coil, the furnace keeps warm air coming out of the vents. And if gas or electric rates change, you move the switchover.
Rebates and running costs
Rebates come off the price, and Xcel changed its heat pump rebates on October 1. See the current rebate amounts. To see what a winter costs on each fuel, read heat pump vs gas furnace running costs.
Send photos of your furnace and outdoor unit and we'll tell you whether your furnace can stay.
Common questions
Can I keep the furnace I have now?
Often, yes. If it's in good shape and its blower can work with a heat pump, we add the heat pump, a new coil and a new thermostat. A photo of the furnace label is usually enough to tell.
What switchover temperature should I set?
Pick it for comfort and backup. At Xcel's October 2026 rates, heat from a 95% gas furnace costs less than heat pump heat at every outdoor temperature, so a lower setting means the heat pump carries more of the winter and the bill goes up a little. You can change it on the thermostat any time.