Heat Pump Versus Electric Resistance, Explained
Why this matters
Many of the customers you talk to about a heat pump already believe electric heat is expensive, and they are right about the electric heat they remember. Baseboard heaters in a 1970s house, a wall furnace with resistance coils, an early heat pump that ran its backup strips all January: those bills were real. The mistake is treating a modern heat pump as more of the same. It is a different machine that happens to plug into the same panel.
The opposite mistake costs you more. A tech who tells a customer "it'll cut your heating bill in half" has made a promise the weather, the utility rates and the ductwork get to break. This card gives you the one number that explains the difference, how to turn it into a comparison with the customer's own rates, and the sentences that stay true after the first winter.
Resistance heat: one in, one out
An electric resistance heater turns electricity into heat in a wire, the way a toaster does. Every kilowatt-hour (kWh) of electricity becomes 3,412 Btu of heat in the room. That conversion is complete: resistance heat is 100 percent efficient at the point of use, and that is also its ceiling. No resistance heater does better than 3,412 Btu per kWh, whatever the box says.
So the efficiency of resistance heat is not the problem. The problem is that electricity is usually priced higher per unit of energy than gas, and resistance heat has no way to make up the difference.
A heat pump moves heat instead of making it
A heat pump uses electricity to run a compressor, which pushes refrigerant through a cycle that absorbs heat from outdoor air and releases it indoors. The electricity pays for moving the heat, not for the heat itself. That is how it delivers more Btu than the electricity contains.
Coefficient of performance (COP) is the ratio of heat delivered to electrical energy used, in the same units. A COP of 1 is resistance heat. A COP of 3 means 3 units of heat delivered for each unit of electricity, which is 10,236 Btu per kWh.
COP falls as the temperature gap grows. The work a heat pump does depends on how far it has to lift heat, from the outdoor coil's temperature to the indoor coil's. The theoretical ceiling (the Carnot limit) is the hot side's absolute temperature divided by the difference between the two. With the indoor coil condensing at 100 F (559.67 R) and the outdoor coil at 10 F, a gap of 90 degrees, the ceiling is 559.67 / 90, about 6.2. Real equipment achieves a fraction of that, and as the outdoor air gets colder the gap widens and the fraction shrinks. Two things follow, both worth saying to a customer:
- A heat pump is most efficient in mild weather and least efficient on the coldest night, which is the night the house needs the most heat.
- Even at its worst, a heat pump that is still running its compressor is above COP 1. A cold-climate unit built to the NEEP cold-climate specification has to show a COP of at least 1.75 at 5 F at maximum capacity.
Seasonal versus instantaneous. COP at one temperature is a snapshot. What the bill reflects is the season. The federal rating for that is HSPF2 (heating seasonal performance factor, under the 2023 DOE test procedure), stated in Btu per watt-hour. Divide HSPF2 by 3.412 to get an approximate seasonal COP. The federal minimum for a split-system heat pump installed since 2023 is 7.5 HSPF2, which is a seasonal COP of about 2.2. HSPF2 is rated in a moderate test climate, so a house in Minnesota will see a lower seasonal figure from the same equipment than the label implies, and one in Georgia a higher one.
Why "electric heat is expensive" was about resistance
Put a price ratio on it. The comparison that matters is how many times more a therm of gas costs than a kWh of electricity on this customer's bills, delivery and supply charges included.
A 95 percent AFUE furnace delivers 95,000 Btu per therm of gas burned. Resistance heat delivers 3,412 Btu per kWh. For resistance to match the furnace on cost, a therm would have to cost 95,000 / 3,412, about 27.8 times a kWh. Few utility territories in the US price them that way, so resistance heat loses nearly everywhere gas is available.
A heat pump at a seasonal COP of 2.2 delivers 7,506 Btu per kWh, so the break-even ratio is 95,000 / 7,506, about 12.7. That is a ratio many territories actually sit near. The heat pump did not make electricity cheaper; it divided the cost of each unit of heat by its COP.
Worked example: turning a customer's two bills into one sentence
A customer with a 95 percent furnace asks what a heat pump will cost to run. You have their last gas and electric bills. Reading the total charge per unit off each (including delivery, excluding the fixed monthly customer charge), a therm costs about 13 times a kWh. That ratio is illustrative; every customer's will differ, and it is the number you compute on site.
HEAT DELIVERED PER UNIT OF ENERGY
furnace, 95% AFUE 95,000 Btu per therm
resistance, COP 1.0 3,412 Btu per kWh
heat pump, COP 2.2 7,506 Btu per kWh
heat pump, COP 3.0 10,236 Btu per kWh
BREAK-EVEN: therm price / kWh price
resistance 95,000 / 3,412 = 27.8
HP at COP 2.2 95,000 / 7,506 = 12.7
HP at COP 3.0 95,000 / 10,236 = 9.3
THIS CUSTOMER: therm costs 13 x a kWh
cost vs furnace = break-even / 13
resistance 27.8 / 13 = 2.14 (more than double)
HP at COP 2.2 12.7 / 13 = 0.98 (about even)
HP at COP 3.0 9.3 / 13 = 0.72 (about 28% less)
Read the last three lines carefully, because they are the conversation. Against this furnace, at these rates, the heat pump runs between about even and about 28 percent less for each unit of heat, depending on whether the season averages a COP near 2.2 or near 3.0. Resistance heat at the same rates would cost 2.14 times the furnace. The heat pump at COP 2.2 costs 1 / 2.2 of resistance, about 45 percent (0.98 / 2.14 from the rounded lines gives 46, the same within rounding): against resistance, the ratio is the COP itself, every time, whatever the gas price.
The sentence that survives the winter: "At your rates, heating with this heat pump should cost about the same as your furnace in a long, cold season and noticeably less in a mild one. It will cost less than half of what baseboard heat would." A colder season pulls the average COP toward the low line; a milder one toward the high line.
What changes the answer
An older furnace. At 80 percent AFUE the furnace delivers 80,000 Btu per therm, so the heat pump at COP 2.2 breaks even at a ratio of 80,000 / 7,506, about 10.7. The same customer at 13 would see the heat pump at 10.7 / 13, about 18 percent less than the furnace. Replacing an old furnace is where the comparison is most favorable.
Leaving gas entirely. If the furnace was the main gas use and the customer drops gas service, the fixed monthly gas charge goes away too, which the per-unit comparison above leaves out on purpose. If they keep gas for one appliance, that charge stays and now buys very little. See related: Keeping Gas for One Appliance.
Strip heat. Most ducted heat pumps carry backup resistance strips. Every hour the strips run is an hour at COP 1. A system with strips staged on too early, a thermostat with deep setbacks that calls for strips on recovery, or a unit undersized for the house drags the seasonal COP toward 1 and the bill toward the resistance line in the box. See related: Backup Heat: Dual Fuel or Resistance, and Heat Pump Sizing for Cold Climate Reference.
Propane or oil instead of gas. Propane is priced per gallon, and a gallon holds about 91,500 Btu, so the furnace line becomes about 86,900 Btu per gallon at 95 percent and the ratio is gallon price to kWh price. Heat pumps usually compare favorably against propane and oil, but compute it rather than say it.
Ducts in an unconditioned attic. Duct losses take their share from either system, but a heat pump's supply air is cooler than a furnace's, so leaky or poorly insulated ducts cost it more comfort. See related: Ductwork When a Heat Pump Replaces a Furnace.
Time-of-use rates. If the customer is on a rate that prices winter evening kWh higher, the single ratio above is an average that hides the expensive hours. See related: Time-of-Use Rates and Equipment Settings.
What not to say
Do not quote a bill. You know the rates and the equipment; you do not know next winter's weather, the customer's thermostat habits, or next year's tariff. A percentage range tied to the customer's own rates is honest; a monthly figure is a promise.
Do not say "three times as efficient" without the temperature. It is true at 47 F and false at 5 F. Say "two to three times as efficient as baseboard over a season, less on the coldest days."
Do not call it free heat from the air. The heat in outdoor air is real, but the customer pays for moving it, and the customer who hears "free" will feel lied to at the first bill.
Do not let the warm-air comparison slide. Heat pump supply air is typically cooler than a furnace's, often in the 90s F against a furnace's 120s or higher. That is a comfort expectation, not an efficiency one; see related: How to Set Expectations for the First Heat Pump Winter.
How to verify the comparison
Recompute the ratio from the customer's bills rather than an average from a website: total charges for the energy line items divided by units used, for each fuel, excluding the fixed monthly charge. Check the proposed unit's HSPF2 and, for a cold climate, its published COP at 5 F and 17 F. If the break-even ratio at the lower COP is close to the customer's ratio, say "about even" and mean it. After the first full winter, compare kWh used for heating against the furnace's prior therms, adjusted for heating degree days, and you will know whether the seasonal COP you assumed was the one the house produced.
References
- US Department of Energy, energy conservation standards and test procedure for central air conditioners and heat pumps (HSPF2, effective 2023)
- Northeast Energy Efficiency Partnerships (NEEP) cold-climate air source heat pump specification
- See related: Heat Pump Cold-Weather Operation Reference; Backup Heat: Dual Fuel or Resistance; How to Set Expectations for the First Heat Pump Winter; Keeping Gas for One Appliance