Heat pump basics: why it stays on so long

You upgraded to a cold-climate heat pump. Now you're staring at a system that runs for an hour straight on a 25°F morning, and the air coming out of the registers feels lukewarm. You're convinced something is wrong. Almost always — nothing is.

How a furnace heats vs. how a heat pump heats

A gas furnace runs flat-out at 110–140°F register temperatures, in short cycles. Five minutes on, twenty minutes off. The air feels hot, you get a quick blast, the room comes up to temperature, the furnace shuts off.

A heat pump moves heat instead of making it. On a 25°F day, it can only push register temperatures into the 90–100°F range — which is cooler than your skin temperature, so the air feels neutral or even cool when you put your hand to a vent. To deliver the same total heat into the room, it has to run for longer.

Long runtimes are a feature

Long, low-intensity cycles are better for comfort: more even temperatures across rooms, much less humidity swing, far fewer hot/cold spots. They're also dramatically more efficient. A heat pump on a properly-set thermostat will run quietly in the background and you'll forget about it.

What is NOT normal

• The auxiliary heat (resistance strips or a backup furnace) running constantly on a mild day. Aux heat is supposed to come on only when outdoor temps are below the heat pump's balance point. If your thermostat shows "AUX" or "EM" indicator at 35°F, something is wrong — usually a thermostat configuration issue.
• The system stuck in defrost. A heat pump occasionally reverses to thaw frost off the outdoor coil. Normal defrost cycles last 5–10 minutes. If you see the outdoor unit frosted over for hours, call us.
• Air actually feeling cold at the registers (below 80°F at the supply during a heat call). That's a sign of low refrigerant or a stuck reversing valve.

Settings that matter

• Don't "set back" a heat pump aggressively. A 4°F night setback that triggers aux heat to recover in the morning costs more than just leaving it alone. 1–2°F is fine.
• Use AUTO fan, not ON. Continuous fan circulates air that's the same temperature as the room, which feels drafty.
• Confirm the lockout temperature. Most installations set the heat pump to lock out below 5–15°F, depending on the model. Below that, the backup heat takes over. Your installer should have programmed this.