Heat Pump vs Gas Furnace Cost Calculator

How it works

1. Heat delivered = therms × 100,000 BTU per therm × AFUE. This is the heat your house actually needs; the rest of the gas went up the flue.
2. Gas cost = therms × price per therm.
3. Heat pump electricity: HSPF2 is BTU of heat per watt-hour over a heating season, so kWh = BTU ÷ (HSPF2 × 1,000) for the share the compressor delivers. The backup share is delivered by resistance strips at 3,412 BTU per kWh (COP 1). Cost = total kWh × price per kWh.
4. Electric resistance (baseboard, strips, an electric furnace) delivers all of it at 3,412 BTU per kWh.
5. Break-even: the electricity price at which the heat pump costs the same as gas is the gas cost divided by the heat pump kWh; the gas price at which they match is the heat pump cost divided by the therms.

An HSPF2 of 8.0 is an average COP of about 2.3, so each kWh moves about 2.3 kWh of heat into the house. Whether that beats gas depends on the ratio of your electricity and gas prices, which is why the same heat pump saves money in one state and costs more in the next.

Worked example

600 therms a year through an 80% furnace delivers 48 MMBtu of heat and costs $840 at $1.40 a therm. A heat pump with HSPF2 8.0 and 10% strip heat needs 5,400 kWh for the compressor plus 1,407 kWh for the strips, 6,807 kWh in all, which is $1,089 at 16¢. Electric resistance would need 14,068 kWh, or $2,251. At these prices the heat pump costs about $249 a year more than the furnace but saves $1,162 against resistance heat; it beats gas once electricity is under about 12.3¢ per kWh or gas is over $1.82 a therm.