Two Heat Sources, One Job: Make Sure Yours Are Ready for Winter

If you've got a dual fuel heating system, you've got two ways to heat your home working together. A heat pump handles the job most of the year, pulling warmth from the outside air even when it's cold out, while a furnace sits in the background as backup. When temperatures drop low enough, usually somewhere between 25 and 35 degrees, your furnace steps in and takes over. The switch happens automatically, so on a normal day you'd never notice it happening.

That's the appeal. You get the lower energy use and efficiency of a heat pump most of the season, plus the reliability of a furnace for those brutal cold snaps when a heat pump alone can't keep up. Neither system has to do all the work, so your home stays comfortable without leaning too hard on one source.

But automatic doesn't mean set it and forget it forever. A system that isn't switching over the way it should can mean uneven heat, longer run times or a furnace working harder than it needs to, and none of that shows up until you're already in the middle of a cold stretch. A few minutes of testing now can save you a surprise later.

Start with the furnace. Switch your thermostat from regular "Heat" to Emergency Heat, sometimes labeled EM Heat depending on your system, then raise the target temperature a few degrees above the room. The outdoor heat pump should stay completely quiet. Within a minute or two, you should hear the furnace fire up and feel warm air coming through the vents. Once you've confirmed it's working, switch the thermostat back to normal.

Now test the heat pump side. If your thermostat has a configurable balance point or lockout setting, not every model does, temporarily set it lower than the current outdoor temperature, then set the thermostat to regular "Heat" and raise the target a few degrees. This time, the outdoor unit should start running, and you'll feel a steadier, milder warmth from the vents instead of the blast you get from a furnace. Once you've confirmed it's working, set the balance point back to where it started.

If either test doesn't go the way it should, that's worth flagging to a contractor before the coldest stretch of the year hits, not during it. Catching a weak changeover now is a lot easier than dealing with a cold house in January.

A few minutes of testing is a small trade for knowing your system will carry you through whatever this winter brings.