First: which system do you have?
Everything below depends on this, and plenty of homeowners are not sure. Here is how to tell in about a minute on a cold day:
- Turn the heat on and walk outside. If the outdoor unit — the one that runs in summer — is also running, you have a heat pump. If it sits dead still, you have a furnace or a boiler.
- Look at your thermostat. A setting labeled Emergency Heat or Em. Heat means heat pump. Only heat pumps have that.
- Look at the indoor unit. A gas flue pipe running out through the wall or roof means combustion. No flue, and a big electrical whip instead, usually means an electric air handler paired with a heat pump.
Dual-fuel systems exist too — a heat pump paired with a gas furnace that takes over when it gets very cold. If that is what you have, treat it like a heat pump for setback purposes.
Why setback works on a furnace and backfires on a heat pump
A furnace has one speed: full blast. Dropping the house to 62°F overnight and bringing it back to 70°F in the morning costs you nothing extra, because the furnace recovers at the same efficiency it always runs at. You genuinely saved the heat you did not use. Deep setbacks are good advice for a furnace.
A heat pump recovers differently. It is designed to run long, steady cycles that gently maintain temperature. Ask it to climb four or five degrees in a hurry and the thermostat decides it is falling behind and switches on the electric resistance strips to help. Those strips cost roughly two to three times as much per unit of heat as the heat pump itself.
So the savings you banked overnight get spent — often with interest — in the twenty minutes it takes to recover in the morning. This is the single most common reason a household switches to a heat pump and sees the bill go up instead of down.
The short version
Furnace: set it back 7–8°F when you are asleep or out. Real savings.
Heat pump: keep setbacks to 2°F or less, or just pick a temperature and leave it there.
The numbers we actually recommend
| Season | Heat pump | Furnace |
|---|---|---|
| Winter, home | 68°F, held steady | 68°F |
| Winter, asleep or away | 66°F (2° setback max) | 60–62°F |
| Summer, home | 75–78°F | |
| Summer, away | 80–82°F — not off | |
On cooling, setback behaves well on any system, so you can be more aggressive in summer than in winter. But do not shut the air conditioning off entirely when you leave for the day in August. In our humidity the house takes on moisture, and the system then has to pull that back out along with the heat, which takes longer and costs more than simply holding 80°F would have.
Every degree does count. Each degree you move the winter setpoint changes heating cost by roughly three percent. Going from 72°F to 68°F is real money over a season — it just needs to be a steady 68, not a sawtooth.
Smart thermostats: helpful, with one condition
A smart thermostat is a good investment on a heat pump only if it is configured for one. The features that matter:
- Heat pump mode with proper staging — the thermostat has to know the difference between the compressor and the strips, and how to stage them.
- Adaptive or intelligent recovery — it starts warming early and gradually so it reaches your target without ever calling the strips.
- An aux heat lockout — you can tell it not to use strips above a set outdoor temperature.
A cheap builder-grade thermostat wired to a heat pump will happily fire the strips any time the room is more than two degrees from setpoint. We have replaced a lot of those and watched the bill drop without touching anything else.
One caution
Do not let an auto-changeover thermostat sit with a narrow gap between heating and cooling setpoints — say heat at 72 and cool at 73. On a shoulder-season day in these mountains the house will bounce between heating and cooling all afternoon. Keep at least 4°F between them.
The fan switch
AUTO is right for most homes most of the time: the blower runs only when the system does. ON runs the blower constantly, which evens out temperatures between rooms and helps a whole-house filter do more work, but it costs you a few dollars a month and, in summer, re-evaporates moisture off the coil back into the house. If your thermostat offers Circulate — the blower runs a portion of each hour — that is usually the better middle ground.
The mistakes that cost the most
- Cranking it to 80 to heat faster. The system has one output. Setting a higher target does not increase it; on a heat pump it only guarantees the strips fire.
- Closing vents in unused rooms. This raises pressure in the ductwork, which pushes more air out through every leak and strains the blower. On most systems it makes things worse, not better.
- Space heaters as a permanent fix. A 1,500-watt heater is pure resistance heat — the most expensive way to make warmth there is. If a room needs one every winter, the room has a problem worth solving properly.
- Leaving it on Emergency Heat after a cold snap because nobody switched it back.
- A thermostat in a bad spot — over a supply register, on an exterior wall, or in direct afternoon sun — reading a temperature the rest of the house never sees. That one we can relocate.
