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Either can use less purchased energy, depending on what happens at the cold-snap temperature. For the same amount of heat delivered indoors, a heat pump uses less input energy when its cold-weather coefficient of performance (COP) remains above 1 and it is not relying heavily on electric resistance backup. A gas boiler’s annual fuel utilization efficiency (AFUE) is a different measure: it estimates fuel-to-heat efficiency over a typical year, not during a single cold hour. So neither technology is the automatic winner; a fair comparison needs the heat pump’s performance and backup use at the temperature in question, alongside the boiler’s fuel input and rating.
What “uses less energy” means
Compare the systems by holding useful heat delivered to the home constant. A heat pump moves heat from outdoors indoors using electricity; its COP is the ratio of useful heating effect to work input. If COP is above 1, the heat delivered exceeds the electrical input because the pump transfers heat rather than creating all of it from electricity. A boiler burns fuel to provide heat, and AFUE expresses how much fuel energy is converted to heat over a typical year.
These figures are not interchangeable. A heat-pump COP describes performance under particular operating conditions, while boiler AFUE is an annual rating. Comparing a heat pump’s COP at a particular outdoor temperature directly with a boiler’s AFUE can mislead unless the time period, delivered heat, backup operation and system boundaries are made clear. DOE explains heat pump operation in its Heat Pump Systems guide and describes boiler efficiency in its boiler purchasing guidance.
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The practical question is therefore not simply whether a COP number is larger than an AFUE percentage. Each number describes a different relationship. COP relates heat delivered to the heat pump’s work input for specified operating conditions. AFUE describes the portion of boiler fuel energy converted to heat over a typical year. For a useful energy comparison, translate each system’s operation into the energy inputs needed to deliver the same amount of heat over the same period, then include any auxiliary or backup heat that contributes.
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The word “energy” also needs a boundary. One comparison may count only electricity or fuel entering the heating equipment; another may account for losses in the distribution system and controls before heat reaches occupied rooms. Either can be useful if the boundary is stated and applied consistently. A comparison that counts heat pump electricity but omits resistance backup, or counts boiler fuel without noting what the efficiency figure represents, can give an incomplete answer.
What changes during a cold snap
Heat-pump capacity and efficiency can fall
As outdoor temperatures drop, a traditional heat pump can lose performance. Cold-climate designs are intended to maintain better capacity and efficiency at lower temperatures, but the category or label alone does not establish how a particular unit will perform at a home’s local design temperature. The relevant evidence is model-specific performance at the outdoor temperature being considered, including defrost operation. DOE discusses conventional and cold-climate performance in its heat pump overview and its Residential Cold Climate Heat Pump Challenge.
That distinction matters because “cold-climate” is not itself a measurement of what a unit will deliver in every location or during every weather event. A homeowner evaluating a cold snap needs performance information for the actual model at the relevant outdoor temperature, not just a general description of the technology. The local design temperature—the outdoor condition used to consider a home’s heating needs—is a useful reference point, but DOE’s cited guidance does not provide a universal temperature threshold at which all heat pumps change over or cease to be suitable.
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Backup heat can change the result
Some heat-pump systems add electric resistance heat as outdoor conditions worsen; dual-fuel systems may instead switch to a gas heating system. Either strategy changes total input energy. Resistance backup supplies heat directly from electricity and can substantially increase electrical use compared with heat-pump operation. In a dual-fuel setup, include the gas system’s fuel use after changeover. There is no universal switchover temperature: it depends on equipment, system design and controls. DOE describes residential heat-pump selection and operating considerations in its residential air-source heat pump acquisition guidance, updated in December 2024.
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In other words, the system may not operate in one mode throughout a cold snap. The heat pump may provide most of the heat in some conditions, while resistance elements or a gas system contribute when conditions worsen. A comparison based only on the heat pump’s COP while it is operating on its own leaves out the energy used by any backup source. For dual fuel, include both the heat pump’s electricity and the gas system’s fuel over the period; for resistance backup, include the electricity used by those elements as well as the heat pump’s input.
Do not infer the changeover point from a generic rule of thumb. It depends on how the equipment is selected and configured and on its controls. To understand a particular installation, ask what source supplies heat at the temperatures being compared and how much of the period each source operates. A label describing the system type cannot answer those installation-specific questions on its own.
Boiler AFUE is not a cold-hour measurement
DOE’s Federal Energy Management Program lists a 90% minimum AFUE for the specified category of residential gas-fired hot-water boilers. That is a stated minimum for the category in that guidance, not the efficiency of every installed boiler or a measurement taken during a cold snap. Its illustrative residential gas-boiler examples use AFUE values of 0.84, 0.90 and 0.97. These examples show variation among boilers; they do not constitute a matched cold-weather test against a heat pump. See DOE’s minimum efficiency requirements guidance and boiler purchasing guidance.
Those boiler figures need careful reading. The 90% minimum refers to the specified gas-fired residential hot-water boiler category in the cited DOE guidance. It should not be described as the efficiency of all boilers in service. The 0.84, 0.90 and 0.97 AFUE values are illustrative examples in DOE’s boiler purchasing material; they are not readings from a single cold snap, nor a matched comparison with a particular heat pump. The examples demonstrate that boiler efficiency varies by model and that the rating needs to be connected to the actual equipment under consideration.
AFUE can still be useful evidence about a boiler. It just does not directly tell you how that specific boiler performed in a particular cold hour. When comparing an existing installation, use the boiler’s available efficiency information and fuel input, and be explicit that AFUE is a typical-year measure. Avoid relabeling an annual rating as a point-in-time cold-weather result.
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How the systems compare on energy
| System or measure | What it tells you | What it does not establish |
|---|---|---|
| Heat-pump COP | Useful heat delivered divided by work input under specified operating conditions. A COP above 1 means delivered heat exceeds electrical input. | Performance at another outdoor temperature, or whole-system use when backup heat is operating. |
| Gas-boiler AFUE | Share of fuel energy converted to heat over a typical year. DOE’s specified residential gas hot-water boiler category has a 90% minimum AFUE; DOE’s illustrative examples are 0.84, 0.90 and 0.97. | A point-in-time efficiency reading during one cold hour, or the performance of every installed boiler. |
| Whole-system energy use | Input energy required to deliver the same useful heat, including relevant backup energy and distribution losses. | A universal winner without data for the actual equipment, controls and conditions. |
A DOE field demonstration reported a seasonal average heating COP of 3.16, with cyclic and frost/defrost losses included. That result belongs to the specific demonstration documented in a source dated 2016; it is not a guarantee for current products, all heat pumps or a particular cold snap. It illustrates why operating conditions and measurement boundaries matter. The demonstration is described in DOE’s High Efficiency Cold Climate Heat Pump field demonstration document.
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The 3.16 figure is useful as a concrete example of a reported field result, not as a prediction for a home. It is a seasonal average for that demonstration, and the source says total COP includes cyclic and frost/defrost losses. That accounting is important: operation over a season can include effects that a single idealized operating point would not show. But the demonstration remains specific to the equipment and conditions covered by its source. It does not prove that another heat pump will achieve the same COP during a different cold snap, nor does it directly compare that installation with a gas boiler.
DOE also notes that space conditioning and water heating consume over 40% of U.S. primary energy. This is broad context about energy use, not evidence that one heating system is more efficient than another in a given home. A national share cannot substitute for the equipment-level data required for a cold-snap comparison.
How to compare two real installations
- Choose the temperature and heat requirement. Identify the outdoor temperature of interest and compare the systems while delivering the same useful heat to the living space. A result for a mild day does not answer a cold-snap question. If the question concerns a particular event, use conditions representative of that event rather than an average season.
- Get the heat pump’s performance at that temperature. Use the particular unit’s capacity and efficiency data for the relevant outdoor condition. Account for defrost operation, cycling and any resistance backup or dual-fuel changeover. A general cold-climate designation is not a substitute for the unit’s data at the temperature being assessed.
- Account for all backup input. If resistance elements operate, include their electricity use. If a gas system takes over, include its fuel use and the heat it supplies. Do not assume a standard switchover point. If the system changes modes over the period, account for the contribution from each mode.
- Use the boiler’s evidence accurately. Record its fuel input and efficiency information. Treat AFUE as a typical-year rating, not as a cold-snap reading. The DOE figures above apply to specified guidance and illustrative examples, not necessarily to the boiler in a particular home.
- Set the system boundary. State whether the comparison includes distribution losses, controls and auxiliary energy. Heat delivered at the equipment is not necessarily identical to heat reaching occupied rooms. Apply the same boundary to both installations so that omitted losses or auxiliary inputs do not favor one system by default.
- Keep energy separate from cost. To compare bills, the energy result must also be paired with current local electricity and gas prices, applicable tariffs and actual operating patterns. Energy consumption alone cannot determine which system costs less.
A useful comparison record can therefore include the outdoor temperature, the amount of useful heat being compared, the heat pump’s performance and capacity at that condition, its defrost and backup operation, the boiler’s fuel input and efficiency evidence, and the system boundary. If the heat pump is dual fuel, note the gas system’s contribution after changeover. If electric resistance heat is used, it cannot be left out just because it is auxiliary. These are not optional refinements when the question is total purchased energy: they determine which inputs are counted.
It is also important to compare like periods. A seasonal COP and annual AFUE summarize performance across different time frames and conditions. They may help describe each technology, but they do not provide a direct answer for a cold snap unless the comparison is reframed around the same period and useful heat output. DOE’s cited sources do not provide a matched head-to-head result for a particular home, so no single percentage or rating can be applied to declare a universal winner.
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Choosing or upgrading a system
If you are selecting a system rather than evaluating an existing one, start with the home’s conditions and the actual equipment, not the technology label alone. For a cold-climate heat pump, seek performance information at the local outdoor temperature of concern and understand whether the system will use resistance backup or a gas system. For a boiler, identify the actual model and its efficiency information instead of relying on a general category minimum or an illustrative DOE example.
Home conditions matter too. DOE recommends weatherization to support optimal savings and comfort when replacing gas heating with a heat pump. That makes an insulation or weatherization assessment a relevant part of planning, alongside a qualified installer’s review of the home and system. Weatherization advice does not itself establish an energy winner or guarantee a particular bill; it supports the conditions under which a heat pump replacement is expected to provide savings and comfort. The DOE heat-pump guidance discusses this recommendation.
Before making a change, ask for a comparison that identifies the expected operating modes and backup strategy rather than assuming the system will behave identically in all weather. Ask which performance data apply at the home’s relevant outdoor temperature, how the system will meet the heat requirement, and what boundary the energy estimate uses. The cited DOE sources do not verify current model-level retail listings or ratings, so product selection should rely on current manufacturer and installer information for the specific equipment being considered.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the available evidence can—and cannot—say
The DOE sources establish how COP and AFUE differ, that traditional heat pumps can lose performance as it gets colder, and that cold-climate designs and backup strategies affect operation. DOE also reports the boiler category minimum and illustrative boiler AFUE values described above. The older field demonstration provides a specific seasonal COP result, not a current product promise.
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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteThose figures do not supply a matched head-to-head result for a particular home during a particular cold snap. To decide which installation uses less energy, you need the heat pump’s cold-weather performance and backup behavior, the boiler’s actual fuel and efficiency information, and a consistent accounting of useful heat and losses. DOE notes that space conditioning and water heating together consume over 40% of U.S. primary energy; that broad context underscores the importance of efficient heating, but does not determine which system wins in an individual home. For a replacement, DOE also recommends weatherization to support optimal savings and comfort when moving from gas heating to a heat pump, as discussed in its heat pump guidance.
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Frequently Asked Questions
Does a heat pump use more electricity when it’s freezing?
It can use more electricity or operate less efficiently as outdoor temperatures drop, and some systems add electric resistance heat when conditions worsen. But the amount depends on the specific heat pump, its performance at that temperature, its controls and whether backup heat operates. Compare the unit’s cold-weather performance and include any backup electricity; a general heat-pump or cold-climate label does not answer the question for every installation.
Is a gas boiler more efficient than a heat pump in very cold weather?
There is no universal winner in the available evidence. A heat pump can use less purchased energy for the same useful heat when its cold-weather COP stays above 1 and it is not relying heavily on resistance backup. Boiler AFUE describes fuel-to-heat efficiency over a typical year, not a point-in-time cold-snap result. A fair comparison needs the actual heat-pump performance and backup use at the temperature in question, along with the boiler’s fuel input and efficiency information.
Can I compare a heat pump’s COP directly with a boiler’s AFUE?
Not as though they were identical measurements. COP is useful heat delivered divided by work input under specified operating conditions; AFUE estimates the share of fuel energy converted to heat over a typical year. Compare the energy inputs needed to deliver the same useful heat over the same period, and state the system boundary and any backup operation.
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1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minuteDoes a cold-climate heat pump guarantee lower energy use in a cold snap?
No. Cold-climate designs target better capacity and efficiency at lower outdoor temperatures than traditional heat pumps, but the category alone does not establish how a particular model performs at a home’s local design temperature. Use model-specific performance information for the temperature of interest and include defrost and backup operation.
What does the DOE field COP of 3.16 mean?
DOE reported a seasonal average heating COP of 3.16 for a specific field demonstration documented in a source dated 2016. The source includes cyclic and frost/defrost losses in total COP. It is evidence about that demonstration, not a guarantee for current equipment, every heat pump or any particular cold snap.
Does using less energy mean the heat pump will cost less to run?
Not necessarily. A cost comparison also needs current local electricity and gas prices, applicable tariffs and the systems’ actual operating patterns. Energy use and energy cost are separate questions; the available DOE sources do not provide a universal cost verdict.
What should I check before replacing a gas boiler with a heat pump?
Check the prospective heat pump’s performance and capacity at the outdoor temperature relevant to your home, how its controls handle backup or dual-fuel changeover, and what energy inputs the estimate includes. DOE also recommends weatherization to support optimal savings and comfort when replacing gas heating with a heat pump. A local weatherization assessment and qualified installer can help evaluate the home, but current model-level performance must be checked for the particular equipment.
The Bottom Line
Bottom line: For the same useful heat, a heat pump can use less purchased energy during a cold snap if its COP remains above 1 and backup heat is limited. A gas boiler’s AFUE is a typical-year fuel efficiency rating, not a cold-hour result, so it cannot be compared directly with a heat pump’s COP as if they measured the same thing. Check the actual equipment at the cold-snap temperature, include all backup energy and relevant losses, and use local tariffs separately if the question is cost rather than energy.
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