Most heat pump thermostats have two installer settings that decide how often backup heat runs: the auxiliary heat lockout and the compressor lockout. They are set once at installation, they rarely appear on the home screen, and the factory defaults are often not the efficient choice. When they are wrong, the system still keeps the house warm. It just costs more to do it, and nobody notices until the bills come in.
Who this helps: homeowners with a heat pump or a dual-fuel (heat pump plus furnace) system, and technicians commissioning or servicing one.
What each setting does
- Auxiliary (aux) heat lockout: above this outdoor temperature, the thermostat will not turn on backup heat, such as electric strips or a furnace. Below it, backup heat is allowed when the heat pump can't keep up.
- Compressor lockout: below this outdoor temperature, the thermostat shuts off the heat pump and uses only backup heat.
- Balance point: the outdoor temperature at which the heat pump's output equals the home's heat loss. Below it, some backup is needed. The Bonneville Power Administration notes that some manufacturers call the aux lockout the "high balance point" and the compressor lockout the "low balance point," which causes plenty of confusion.
Both lockouts need an outdoor temperature. This comes from an outdoor sensor, a weather feed over Wi-Fi, or the outdoor unit's control board. If the thermostat has no outdoor reading, the lockout options may not even appear, and backup heat can run at any temperature.
What efficiency programs require
Utility programs with heat pump commissioning rules are consistent on electric backup. The Bonneville Power Administration heat pump commissioning specification requires the aux (strip) heat lockout to be set at 35°F or lower. It says the compressor lockout should be disengaged so the compressor runs at all outdoor temperatures, and that wrong lockout settings cause the majority of its inspection failures. Energy Trust of Oregon applies the same 35°F rule. ENERGY STAR requires certified smart thermostats to report how much resistance heat heat pump homes use, in 5°F outdoor bins from 0 to 60°F, because overuse of strip heat is a known way savings get lost.
Field check: some installer menus ship with the aux lockout at 70°F or set to off/disabled. Either one effectively lets strip heat run whenever the thermostat thinks recovery is too slow, even on a mild 50°F day.
Dual fuel is a different decision
With a gas furnace as backup, the question changes from "how do I keep strip heat off" to "below what temperature is gas cheaper than the heat pump." That temperature is the economic balance point. It depends on your electric and gas rates and on how efficient your heat pump is at each outdoor temperature. Our winter heating cost outlook shows how to calculate the break-even COP.
Defaults vary widely. A California Energy Commission staff survey of thermostats found dual-fuel switchover defaults ranging from 35°F to 50°F, with 40°F the most common. It adopted 40°F as the assumed lockout in its 2025 energy code compliance software.
What a New Jersey field study found
A 2026 ACEEE summer study paper by DNV and New Jersey Natural Gas evaluated the utility's hybrid heat program, which pairs heat pumps with gas heating. At 16 inspected homes:
| Finding | Result |
|---|---|
| Aux (gas) heat lockout disabled | 8 of 16 homes |
| Compressor lockout disabled | 3 of 16 homes |
| Most common compressor lockout | 40°F |
| Average compressor lockout (where enabled) | 35°F |
| Lowest temperature the heat pumps could operate at | 5°F |
| Average gas savings, 10 submetered homes | 65 therms (23% of input energy) |
The authors found that savings were highest at properly commissioned homes where the compressor lockout was enabled and set below the calculated economic balance point, so the heat pump wasn't shut off too early. Deeper thermostat setbacks did not appear to help and may have reduced savings, because big morning recoveries pulled in backup heat. Few contractors reported using the program's balance-point calculator.
How to check your settings
- Find the installer or advanced menu. Look for words like "lockout," "balance point," "aux heat max outdoor temperature," or "switchover." The exact path is in your thermostat's installation guide.
- Confirm there is an outdoor temperature source. This can be a sensor, a Wi-Fi weather feed, or the outdoor unit. Without one, lockouts don't work.
- All-electric with strip heat: the program guidance above sets the aux lockout at 35°F or lower and leaves the compressor running at all temperatures, as long as the system is sized for the load.
- Dual fuel: set the switchover near your calculated economic balance point, and check it against the heat pump's published capacity at that temperature.
- Use modest setbacks. Keep setbacks small, and turn on any "smart recovery" or adaptive recovery feature so the morning warm-up doesn't trigger backup heat.
- Watch the reports. Many connected thermostats show aux heat runtime. Aux hours on mild days point to a setting problem.
Limitations
Lockouts only work if the heat pump is sized for the home. The Bonneville Power Administration guidance warns that an undersized system can cause comfort complaints once strip heat is locked out. The New Jersey study is small: 16 homes inspected and 10 submetered, all in one utility program. Some newer thermostats choose lockouts automatically based on how the system performs. Their results depend on the algorithm and the data the thermostat receives, and they still need to be configured correctly for the equipment type. Some outdoor units also have their own low-ambient cutouts, separate from the thermostat. Always follow the equipment manufacturer's installation instructions.
Not an endorsement: this article explains thermostat settings that appear across many products and does not recommend any brand. HVAC Zone Inc is a multi-brand dealer, and the Hub is brand-neutral.
Not sure how your heat pump or dual-fuel system is configured? Request a consultation with HVAC Zone for a site-specific assessment.