Estimate the outdoor temperature where your heat pump and backup furnace or boiler cost about the same.
Advanced options
| Outdoor temp. | Heat pump | Backup | Lower cost |
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Table of contents
How to use our Dual Fuel Heat Pump Balance Point Calculator
- Choose the Heat pump performance profile that best matches your system, or leave it on Cold-climate if you are making a first estimate.
- Choose the Backup fuel type, then enter Electricity price, Backup fuel price, and Backup heat efficiency from your bill or equipment label.
- If you have a manufacturer performance table, open Advanced options and enter all three values: Custom COP at 47 F, Custom COP at 17 F, and Custom COP at 5 F.
- Select Calculate and read Estimated switch-to-backup outdoor temperature first; warmer than this usually favors the heat pump, and colder than this usually favors backup heat.
- Sanity-check the result with Heat pump cost advantage at 17 F and Outdoor temperature cost comparison. If one fuel price seems far from your bill, fix that input before using the switch temperature.
Definitions
COP: Coefficient of performance. It means how many units of heat the heat pump makes from 1 unit of electricity. A COP of 3 means the heat pump makes about 3 units of heat for each unit of electricity it uses.
AFUE: Annual fuel utilization efficiency. It is the percent of fuel heat that reaches the house as useful heat.
MMBtu: One million British thermal units. The calculator uses $/MMBtu so electricity, natural gas, propane, and heating oil can be compared on the same delivered-heat basis.
Economic balance point: The outdoor temperature where the heat pump and backup heat have the same estimated cost per delivered MMBtu.
Heat pump cost advantage at 17 F: Backup heat cost minus heat pump cost at 17 F. Positive means the heat pump is cheaper; negative means backup heat is cheaper.
Common mistakes and quick fixes
Mistake: Entering the monthly electric bill total in Electricity price.
Fix: Use the all-in price per kWh, including supply and delivery charges if your bill shows them.
Mistake: Using gallons for natural gas in Backup fuel price.
Fix: If Backup fuel type is natural gas, enter Backup fuel price in $ per therm; use $ per gallon for propane or heating oil.
Mistake: Typing 0.95 in Backup heat efficiency when the furnace AFUE is 95 percent.
Fix: Enter 95, not 0.95, because Backup heat efficiency is a percent input.
Mistake: Filling only Custom COP at 47 F because that is the easiest rating point to find.
Fix: Enter Custom COP at 47 F, Custom COP at 17 F, and Custom COP at 5 F together, or leave all three blank.
Mistake: Treating a negative Heat pump cost advantage at 17 F as an error.
Fix: Negative means backup heat is estimated to cost less than the heat pump at 17 F.
Limitations & Key Assumptions / Boundary Conditions
- This is an economic balance point, not a thermal balance point. It compares operating cost, not whether the heat pump has enough capacity to heat the house.
- Built-in heat pump profiles are planning defaults. Custom COP points from your own equipment data sheet can give a better estimate.
- Actual heat pump COP can change with defrost cycles, airflow, duct losses, thermostat staging, indoor temperature, and installation quality.
- Utility bills may include fixed monthly charges, taxes, riders, or time-of-use prices. Use the variable energy price when you want a pure operating-cost comparison.
- Backup fuel heat content is treated as a standard planning value: natural gas in therms, propane in gallons, and No. 2 heating oil in gallons.
- The switch temperature is searched over the checked outdoor range only. If one system is cheaper across that range, the calculator reports that instead of inventing a crossover.
Methodology
Cost basis
The calculator converts both heating options to cost per delivered MMBtu, which means cost for 1 million Btu of useful heat reaching the home. That lets electricity and fuel be compared on the same heat-output basis.
backup_cost_per_mmbtu = fuel_price / (fuel_heat_content_mmbtu_per_unit * afue_decimal)
Fuel heat content is 0.1 MMBtu per therm for natural gas, 0.0915 MMBtu per gallon for propane, and 0.1385 MMBtu per gallon for heating oil. The AFUE decimal is Backup heat efficiency divided by 100.
hp_cost_per_mmbtu(T) = electricity_rate * 293.07107 / cop(T)
The value 293.07107 is the number of kWh in 1 MMBtu of energy. COP is unitless, so a higher COP lowers the heat pump cost.
COP curve
If all three custom COP fields are filled, the calculator uses Custom COP at 5 F, Custom COP at 17 F, and Custom COP at 47 F. If they are blank, it uses the selected Heat pump performance profile. COP between rating points is estimated with a straight line.
cop(T) = cop_low + (T - temp_low) * (cop_high - cop_low) / (temp_high - temp_low)
Switch temperature
The backup cost is converted into the COP the heat pump must reach to tie the backup system cost.
required_cop = electricity_rate * 293.07107 / backup_cost_per_mmbtu
The Estimated switch-to-backup outdoor temperature is the temperature where the interpolated COP equals that required COP. If the curve does not cross within the checked range, the output note says which option is estimated cheaper across the range.
cost_advantage_at_17f = backup_cost_per_mmbtu - hp_cost_per_mmbtu(17)
Mini-example
With natural gas at $1.50 per therm and Backup heat efficiency of 95 percent, backup heat costs $15.79 per delivered MMBtu. With Electricity price of $0.16/kWh and the cold-climate profile COP of 2.6 at 17 F, heat pump heat costs $18.04 per MMBtu at 17 F. The required COP is 2.97, so the cold-climate profile reaches the cost match at about 29.3 F. The Heat pump cost advantage at 17 F is -$2.25/MMBtu, meaning backup heat is estimated cheaper at 17 F.