Turning the thermostat down at night is old advice that works well with a gas furnace. With a heat pump it can backfire. In Tacoma, where winter mornings usually sit between 35 and 45°F, the setback itself is often the thing that turns on expensive electric backup heat. This guide explains why, shows the math, and gives you settings that actually lower the bill.
Why furnace logic does not carry over
A gas furnace delivers the same blast of heat whether it is recovering 2 degrees or 8 degrees, so a deep setback simply means it runs longer in the morning. A heat pump is different. It moves heat rather than making it, and its output is modest and steady. When you ask it to climb 6 or 8 degrees quickly, most thermostats decide the heat pump is too slow and bring on the backup electric strips, sometimes called auxiliary heat.
Those strips are simple resistance heaters. One kilowatt hour of electricity gives one kilowatt hour of heat. A heat pump on a 40°F morning typically delivers roughly 3 units of heat for every unit of electricity, often written as a coefficient of performance (COP) around 3. That ratio is the whole story.
The recovery math
Here is a simple illustration using round numbers. Your actual figures depend on the house, the equipment, and your utility rate.
| Scenario | Heat delivered | Electricity used |
|---|---|---|
| Heat pump alone, COP about 3 | 30,000 BTU (about 8.8 kWh of heat) | About 2.9 kWh |
| Typical 10 kW backup strips running 1 hour | 34,000 BTU (10 kWh of heat) | 10 kWh |
| Strips running 20 minutes during a fast morning recovery | About 11,400 BTU | About 3.3 kWh |
Notice the last row. Just 20 minutes of strip heat during recovery uses more electricity than a full hour of the heat pump working on its own. A deep overnight setback on a mild Tacoma night saves only a little, because the house loses heat slowly when it is 40°F outside. One strip heat event in the morning can wipe out the whole night of savings.
What actually works in Tacoma
1. Keep setbacks to 2 or 3 degrees
A small setback still trims runtime overnight, and the heat pump can recover from it without help. Most of our customers land on 68°F during the day and 65 or 66°F overnight.
2. Turn on smart or adaptive recovery
Most heat pump thermostats offer a setting that starts recovery early and ramps slowly, so the house reaches temperature on time using the compressor only. It might be called adaptive recovery, smart recovery, or early start. Turn it on.
3. Set an outdoor auxiliary heat lockout
If your thermostat has an outdoor temperature sensor or reads local weather, you can tell it not to use strips above a set outdoor temperature. In our climate, a lockout somewhere around 30 to 35°F keeps strips off on typical mornings while still allowing them during a real cold snap. Your installer should confirm the right number based on your heat pump’s capacity and your home’s heat loss.
4. Drop the setback during cold snaps
A few times each winter, Fraser River outflow winds push Arctic air into Pierce County and lows fall into the teens or 20s. On those nights, hold one steady temperature. A heat pump is already working near its limit, and any recovery will lean on backup heat.
5. Leave ductless systems alone
Ductless mini splits, such as Mitsubishi Electric and Daikin units, are designed to run continuously at low speed. Most have no strip heat at all, so setbacks mostly just make rooms feel cold longer. Pick a comfortable setting and leave it.
How to tell if your strips are running
Most thermostats display “Aux,” “Auxiliary heat,” or “Emergency heat” when strips are on. Some apps, including American Standard‘s thermostat apps, the Mitsubishi Electric Comfort app, and the Daikin One app, log runtime by stage. If you see auxiliary heat every morning on 40°F days, the setback or the staging settings need adjusting, or the system may need service. A big jump in your winter electric bill with no change in habits is another clue.
Thermostat setback FAQ
Is it ever worth doing a deep setback on a heat pump?
If you are away for several days, yes. A setback of 8 to 10 degrees while the house is empty saves energy, as long as you bring it back up slowly or a day ahead of your return.
Does a smart thermostat automatically know I have a heat pump?
Only if it was wired and configured for one. Check the installer settings for heat pump type, number of auxiliary stages, and the reversing valve setting. A thermostat set up as a furnace control will make bad decisions.
Why does my heat pump run all the time on cold days?
That is often normal. Modern variable speed heat pumps are designed to run long and slow. Long runtime with steady comfort is efficient. Long runtime with the house losing temperature is a reason to call.
What about dual fuel systems with a gas furnace?
Dual fuel systems switch to the furnace below a set outdoor temperature, so strip heat is not the concern. Small setbacks still work best on the heat pump side, while the furnace handles recovery on colder mornings.
Want your thermostat set up right?
GreenFlow Heating & Cooling can check your heat pump thermostat staging, recovery, and lockout settings during a service visit anywhere in Tacoma and Pierce County. Call (253) 370-8641 or send us a message.