Compare heat pump and gas furnace heating bills using your heat need, utility rates, and equipment efficiency.
Table of contents
How to use our Heat Pump vs Furnace Calculator
- Enter Heat needed for the season in million Btu. Use delivered heat, not the furnace input size.
- Choose Heat pump efficiency type, then enter either Heat pump HSPF2 or Heat pump COP from the heat pump rating or estimate.
- Enter Furnace AFUE, Electric rate, and Natural gas price using the variable rates from your bills.
- Open Advanced options only if you want payback or a multi-year comparison using installed costs and price changes.
- Check the output by comparing Heat pump electricity used and Furnace gas used with past bills. If either looks far from your real winter use, recheck the heat need and rates.
Definitions
Heat needed for the season: The useful heat delivered to the home during the heating season, measured in million Btu.
HSPF2: A seasonal heat pump efficiency rating in Btu per Wh. Higher HSPF2 means less electricity for the same heat.
COP: Coefficient of performance, a ratio of heat delivered to electric energy used when both are measured in the same energy units [1].
AFUE: Annual fuel utilization efficiency. It is the percent of furnace fuel heat that becomes useful heat in the home.
Therm: A common natural gas billing unit equal to 100000 Btu.
Break-even COP: The heat pump COP that makes the heat pump heating cost equal to the furnace heating cost for the entered rates and AFUE.
Simple payback: The first year when cumulative bill savings recover the extra installed cost of the heat pump.
Common mistakes and quick fixes
Mistake: Entering furnace input size as Heat needed for the season.
Fix: Use delivered seasonal heat in million Btu, or estimate it from past fuel use and Furnace AFUE.
Mistake: Mixing up Heat pump HSPF2 and Heat pump COP.
Fix: Set Heat pump efficiency type first, then fill only the matching efficiency field shown by the calculator.
Mistake: Typing Furnace AFUE as 0.95 instead of 95.
Fix: Enter Furnace AFUE as a percent, so a 95% furnace is entered as 95.
Mistake: Using an Electric rate or Natural gas price that leaves out delivery charges that change with use.
Fix: Use the all-in variable price from your bill when possible, such as $ per kWh and $ per therm.
Mistake: Entering only one of Heat pump installed cost or Furnace installed cost.
Fix: Enter both installed costs, or leave both blank if you only want yearly heating bills.
Mistake: Reading Annual bill change with the heat pump as always positive savings.
Fix: A negative Annual bill change with the heat pump means the heat pump costs more to run for your entered prices.
Limitations & Key Assumptions / Boundary Conditions
- The comparison covers heating energy only. It does not include cooling savings, repairs, maintenance, rebates, taxes, financing, comfort changes, backup heat, or equipment lifespan.
- Heat needed for the season must be a delivered heat estimate. If that value is too high or too low, every cost and energy result shifts by the same proportion.
- Electric rate and Natural gas price should be variable rates that change with usage. Fixed monthly customer charges are not included.
- HSPF2 is a seasonal rating. Real heat pump performance can change with outdoor temperature, duct losses, thermostat settings, and defrost operation.
- Furnace AFUE is treated as the seasonal fuel-to-heat efficiency. Actual delivered heat can differ if ducts leak or if the system is poorly sized.
- Years to compare is limited to a simple projection. Price changes are applied once per year, and no discount rate or fuel switching fee is used.
- Simple payback is shown only when both installed costs are entered and cumulative yearly savings can recover the extra heat pump cost within the comparison years.
Methodology
Core heating cost math
The calculator first converts the entered Heat needed for the season from million Btu to Btu. If HSPF2 is selected, it converts useful heat directly to electricity. If COP is selected, it uses 3412 Btu per kWh for electric energy.
heat_pump_kwh = annual_heat_mmbtu * 1000000 / (hp_hspf2 * 1000)
heat_pump_kwh = annual_heat_mmbtu * 1000000 / (hp_cop * 3412)
annual_heat_pump_cost = heat_pump_kwh * electric_rate
For the gas furnace, the calculator divides delivered heat by AFUE to estimate fuel heat, then converts Btu to therms.
furnace_therms = annual_heat_mmbtu * 1000000 / ((furnace_afue_percent / 100) * 100000)
annual_furnace_cost = furnace_therms * gas_price_per_therm
annual_savings_hp_vs_furnace = annual_furnace_cost - annual_heat_pump_cost
A positive annual savings result means the heat pump has the lower yearly heating bill. A negative result means the furnace has the lower yearly heating bill.
Break-even efficiency
The break-even result solves for the heat pump COP where the cost per delivered million Btu is the same as the furnace cost per delivered million Btu.
break_even_cop = (1000000 * electric_rate) / (3412 * (10 / (furnace_afue_percent / 100) * gas_price_per_therm))
break_even_hspf2 = break_even_cop * 3.412
If the heat pump's actual seasonal COP is above the break-even COP, the heat pump is cheaper to run. If its actual seasonal COP is below that value, the furnace is cheaper to run.
Installed cost and payback math
When both installed costs are entered, the calculator adds each installed cost to projected yearly heating costs. Electric and gas price changes are applied separately for each year.
projected_total_difference = furnace_total_cost - heat_pump_total_cost
yearly_savings = escalated_furnace_cost - escalated_heat_pump_cost
simple_payback_years = first year where cumulative yearly_savings >= hp_installed_cost - furnace_installed_cost
A positive projected total difference means the heat pump costs less over the selected years. A negative value means the furnace costs less over the selected years.
Worked mini-example
Suppose the home needs 50 million Btu of heat, the heat pump is HSPF2 9.5, electricity costs $0.17 per kWh, the furnace is 95 AFUE, and gas costs $1.50 per therm. The heat pump uses 50 * 1000000 / (9.5 * 1000) = 5263.16 kWh, so its heating cost is about $894.74. The furnace uses 50 * 1000000 / (0.95 * 100000) = 526.32 therms, so its heating cost is about $789.47. Annual bill change with the heat pump is $789.47 - $894.74 = -$105.26, so the furnace is cheaper to run in that example.