Heat Pump vs Gas Furnace Cost Calculator
Compare yearly heating costs.
Special
Dual Fuel Switchover Temperature Calculator
A dual fuel system should hand over from the heat pump to the furnace when the furnace becomes the cheaper source of heat. Enter your prices and the heat pump’s rated COP to estimate that economic balance point.
How it works
- Choose the furnace fuel and enter your electricity and fuel prices from recent bills.
- Enter the furnace efficiency (AFUE) and the heat pump’s COP at 47 °F and 17 °F from its data sheet.
- Read the estimated economic switchover temperature and compare costs across temperatures in the table.
- Share the result with your HVAC contractor when setting the dual fuel lockout or balance point.
Formula
Furnace $/MMBtu = fuel price × 1,000,000 ÷ (Btu per unit × AFUE) Break-even COP = electricity price × 1,000,000 ÷ (3,412 × furnace $/MMBtu) COP(T) = COP₁₇ + (T − 17) × (COP₄₇ − COP₁₇) ÷ 30 Switchover T = 17 + (break-even COP − COP₁₇) × 30 ÷ (COP₄₇ − COP₁₇)
A heat pump costs the same per unit of heat as the furnace when its COP equals the break-even COP. Heat pump COP falls as it gets colder, so the calculator draws a straight line through the two AHRI rating points (17 °F and 47 °F) and finds the temperature where the line crosses the break-even COP. Above that temperature the heat pump is cheaper; below it, the furnace.
Example
A propane dual fuel system with a 95% furnace, propane at $2.60/gal and electricity at $0.16/kWh. The heat pump is rated COP 3.8 at 47 °F and 2.6 at 17 °F.
Inputs
- Furnace fuel
- Propane
- Electricity price
- $0.16 / kWh
- Propane price
- $2.6 / gal
- Furnace efficiency (AFUE)
- 95 %
- Heat pump COP at 47 °F
- 3.8
- Heat pump COP at 17 °F
- 2.6
- Show temperatures in
- °F
Result
Economic switchover temperature≈ -9 °FHeat pump below this cost, furnace cheaper in colder weather
Break-even COP1.57
Furnace cost per MMBtu$29.93
Heat pump cost per MMBtu at 47 °F$12.34
Economic vs. thermal balance point
The economic balance point is about cost: the temperature where either system delivers heat for the same price. The thermal balance point is about capacity: the temperature where the heat pump can no longer keep the house warm on its own. A dual fuel control should switch to the furnace at whichever temperature is higher, or the home either overpays or gets cold.
Because electricity and fuel prices change, it is worth re-running the numbers each season. Time-of-use electricity rates can move the switchover point by 10 °F or more between peak and off-peak hours.
Frequently asked questions
What is a typical dual fuel switchover temperature?
With natural gas it commonly lands somewhere around 20–45 °F, and where gas is very cheap relative to electricity the furnace can be cheaper in all heating weather. With propane or oil, heat pumps usually stay cheaper down to much colder temperatures. Your own prices matter more than any rule of thumb.
Where do I find the COP at 47 °F and 17 °F?
On the AHRI Directory certificate for the matched system or in the manufacturer’s extended performance data. Some sheets list heating capacity and power instead; COP = capacity (Btu/h) ÷ (watts × 3.412).
Should I set my lockout to exactly this temperature?
Use it as a starting point. The control must also respect the thermal balance point, defrost behavior and comfort; your HVAC contractor can confirm the final setting.
Why do propane systems switch over at lower temperatures?
Propane usually costs more per million Btu than natural gas, so the heat pump stays cheaper even when its COP drops in cold weather.