A monthly bill starts with heat demand
A heat pump’s electricity use is not determined by tonnage alone. The house’s heat requirement, outdoor conditions, equipment performance, controls, and backup use all matter. A useful estimate separates heat delivered from electricity consumed and clearly states which loads are included.
EIA’s unit conversion lets you convert Btu to kWh of heat: divide Btu by approximately 3,412. Then divide that thermal energy by an assumed period-average COP to estimate compressor-system electrical energy. COP is dimensionless; it compares heat output and electric input using equivalent energy units.
A transparent monthly example
Assume for illustration that the house needs 6 million Btu of delivered heat in a month. That equals about 1,758 kWh of thermal energy. Assume all of it is provided by the heat pump and the electrical rate is $0.18/kWh.
| Assumed average COP | Estimated electrical energy | Estimated heating electricity cost |
|---|---|---|
| 2.0 | 879 kWh | $158 |
| 2.5 | 703 kWh | $127 |
| 3.0 | 586 kWh | $106 |
| 3.5 | 502 kWh | $90 |
These are calculated scenarios, not an average heating bill. They exclude consumption outside the specified system boundary. If blower, standby, or defrost energy is not already represented in the COP assumption, account for it explicitly rather than silently assuming it is zero.
The heat pump versus gas calculator accepts heating demand and efficiency inputs. You can use its heat pump result independently even when you are not considering a furnace.
Add backup without double counting
Suppose 15% of that same month’s useful heat is supplied by electric resistance backup and 85% by the heat pump at COP 3. The heat pump needs about 498 kWh and resistance backup about 264 kWh, for a total near 762 kWh, or $137 at $0.18/kWh. Do not calculate the heat pump as supplying 100% of the heat and then add backup as if it supplies extra demand.
Alternatively, if you have reliable metered backup consumption, add those kWh directly to the measured or modeled compressor-system consumption. Be consistent about which method you use. PNNL’s cold-climate guide explains why load matching and auxiliary heat belong in the equipment design.
Where to obtain the inputs
Ask the installer for a heating-load calculation and an explanation of seasonal energy assumptions. A design load in BTU/h at one outdoor temperature is a rate, not a monthly total. Multiplying that peak rate by every hour in a winter month usually overstates demand because the house rarely remains at the design condition continuously.
Historical fuel bills can inform a model, but first separate water heating, cooking, and other uses. A qualified energy professional can account for weather and existing heating efficiency. For an existing heat pump, equipment monitoring and utility interval data can improve the estimate, although whole-house electricity includes many other appliances.
Use the exact utility tariff or a clearly identified blended rate. Record whether prices include variable delivery charges and whether time-of-use rates apply. Leave fixed account fees outside an incremental heating comparison unless the project changes those fees.
Why the coldest month can surprise you
A colder month increases building heat demand. Equipment efficiency and available capacity may also change, and supplemental heat may supply a greater share. A higher bill can therefore reflect several interacting factors rather than one defective component. ENERGY STAR defines HSPF2 as a standardized seasonal measure; it is not a guarantee of the COP in a particular cold month.
Compare weather, billing days, rates, indoor settings, and auxiliary-heat operation before judging a bill. If comfort declines, error messages appear, or backup seems inconsistent with the commissioned setup, ask for service rather than changing installer controls yourself.
Keep an estimate log
Save the demand assumption, COP range, backup share, rate, and resulting kWh. After each bill, update the inputs supported by evidence and keep uncertain inputs visible. This is more informative than assigning the home a single permanent “heat pump monthly cost.”
Read backup-heat options for system differences and HSPF2 explained for rating interpretation. The strongest estimate is one whose uncertainty you can explain and reduce over time.