Most dual-fuel systems switch from the heat pump to the furnace at whatever temperature the installer typed in, often 30°F, 35°F or 40°F. The right number comes from your prices, not a rule of thumb, and it can sit anywhere from the low 40s to below zero. Here is how to find yours.
The Short Answer
Switch to the furnace at the higher of two temperatures:
- the temperature where heat from the heat pump starts costing more than heat from the furnace (the economic balance point), and
- the temperature where the heat pump can no longer keep the house warm by itself (the thermal balance point).
With natural gas at $1.70 a therm, electricity at 18¢ and a 95% furnace, the economic balance point is about 32°F for a typical single-stage heat pump and about 20°F for an inverter (variable-speed) one. With propane or heating oil it usually falls in the single digits or teens, low enough that the heat pump's capacity, not price, decides. The dual-fuel switchover calculator works out both points for your system.
Switchover Temperature by Gas and Electricity Price
Economic balance point with a 95% condensing furnace. In each cell the first figure is a typical single-stage heat pump (COP 3.6 at 47°F, 2.3 at 17°F) and the second, smaller figure an inverter heat pump (COP 4.2, 2.8 and 2.1 at 5°F).
| Gas price | 12¢/kWh | 18¢/kWh | 24¢/kWh | 30¢/kWh |
|---|---|---|---|---|
| $1.00/therm | 41°F 28°F | 50°F+ 50°F+ | 50°F+ 50°F+ | 50°F+ 50°F+ |
| $1.50/therm | 15°F 7°F | 41°F 28°F | 50°F+ 50°F+ | 50°F+ 50°F+ |
| $2.00/therm | 2°F -2°F | 22°F 12°F | 41°F 28°F | 50°F+ 46°F |
"50°F+" means the furnace is cheaper through nearly all heating weather, so the heat pump earns its keep mainly on mild days and for cooling.
The pattern is simple: the switchover rises as electricity gets pricier relative to gas. Cheap gas and expensive power push it into the 40s or higher; expensive gas and cheap power push it below 20°F.
An Older 80% Furnace Changes the Answer
A non-condensing furnace wastes about a fifth of its fuel, so its heat costs more and the heat pump stays ahead longer. The same table with an 80% furnace:
| Gas price | 12¢/kWh | 18¢/kWh | 24¢/kWh | 30¢/kWh |
|---|---|---|---|---|
| $1.00/therm | 29°F 17°F | 50°F+ 47°F | 50°F+ 50°F+ | 50°F+ 50°F+ |
| $1.50/therm | 7°F 1°F | 29°F 17°F | 50°F+ 37°F | 50°F+ 50°F+ |
| $2.00/therm | -4°F -7°F | 13°F 5°F | 29°F 17°F | 45°F 32°F |
At $1.70 gas and 18¢ power, the single-stage switchover drops from about 32°F to about 22°F — ten degrees of extra heat pump hours on every cold night.
Propane and Heating Oil: Let the Heat Pump Run
Delivered fuels cost so much more per BTU that the heat pump stays cheaper far into the cold. Economic balance point with a 95% propane furnace or an 85% oil furnace:
| Fuel | 15¢/kWh | 20¢/kWh | 25¢/kWh |
|---|---|---|---|
| Propane $2.00/gal | 8°F 2°F | 23°F 13°F | 37°F 25°F |
| Propane $2.50/gal | -1°F -5°F | 11°F 4°F | 23°F 13°F |
| Propane $3.30/gal | -9°F -11°F | 0°F -5°F | 8°F 2°F |
| Heating oil $3.50/gal | -2°F -6°F | 9°F 3°F | 21°F 11°F |
| Heating oil $4.00/gal | -6°F -9°F | 4°F -2°F | 14°F 6°F |
This matches the Northwest Energy Efficiency Alliance's 2026 analysis of dual-fuel controls, which found that a Montana home on delivered propane had the lowest bill with the heat pump carrying the load down to 20°F or below — while the same house on piped gas did best switching at 40°F. With propane or oil, set the changeover at the thermal balance point: as low as your heat pump can keep the house comfortable.
Finding the Thermal Balance Point
Heat pump output falls as it gets colder while the house needs more heat. The temperature where those lines cross depends on the heat pump's capacity at 17°F (on its AHRI certificate) and your home's heat loss. A typical 3-ton single-stage unit puts out about 60% of its rated heat at 17°F, so in a house that needs 40,000 BTU per hour at 5°F, it runs out of capacity around 26°F. A cold-climate unit holding most of its capacity at 17°F can carry the same house below 10°F.
If the thermal balance point is above your economic one, the switchover belongs at the thermal one: below it, the furnace has to run anyway. Setting the changeover lower just means the house cools off before the furnace kicks in.
Three Mistakes That Cost Money
- Leaving the default. A 40°F switchover with cheap power and expensive gas, or with propane, throws away the heat pump's best hours. NEEA's Portland case burned three times as much gas at a 40°F setting as at 30°F.
- Electric strips on a dual-fuel system. If the air handler also has resistance strips, make sure they're locked out. At 18¢ they cost about $53 per million BTU — three times the furnace. The aux heat calculator shows what they add.
- Setting it once and forgetting it. A winter rate change, a time-of-use plan, or a gas price jump can move the economic balance point by 10°F or more. Recheck each fall.
Your thermostat may call the setting balance point, compressor lockout, dual-fuel changeover or breakpoint; it's usually in the installer or advanced menu.