A heat pump normally uses less delivered energy than a gas boiler. The International Energy Agency (IEA) says current heat pumps are typically three to five times more energy efficient than gas boilers. That does not automatically make every heat pump cheaper to run: electricity can cost several times more per kilowatt-hour than gas, and a poorly designed installation can have a much lower seasonal performance than its headline rating.
For a fair decision, separate three questions: how much input energy the system needs, what that energy costs on your tariff, and how well the equipment performs in your home. The sections below show how to calculate each one.
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What “uses less energy” means
A gas boiler burns fuel and releases heat. A heat pump uses electricity to move heat from outdoor air or the ground into the building. Because it transfers existing heat rather than creating all of it by combustion, a heat pump can deliver several kilowatt-hours of heat for each kilowatt-hour of electricity.
| System | How efficiency is expressed | Figures cited by the sources | What the figure means |
|---|---|---|---|
| Gas boiler | Combustion efficiency | About 75% for an older boiler due for replacement; about 85% for a typical new boiler; cited guidance spans roughly 75–92% | To deliver 1 kWh of heat, the boiler needs more than 1 kWh of gas because some heat leaves in the exhaust and through other losses. |
| Air-source heat pump | COP for a test condition; SPF or SCOP over a season | IEA 2024 model: 250% efficiency; Energy Saving Trust monitored average SPF: 2.45 | A seasonal SPF of 2.45 means 2.45 kWh of heat delivered for each kWh of electricity used over the monitored period. |
| Ground-source heat pump | COP for a test condition; SPF or SCOP over a season | IEA 2024 model: 320% efficiency; Energy Saving Trust monitored average SPF: 2.82 | The ground is usually a more stable heat source than winter air, but ground loops require suitable land and more installation work. |
The IEA’s broad three-to-five-times comparison describes energy efficiency, not a guarantee of a three-to-five-times reduction in your bill. Your bill also depends on the price ratio between electricity and gas and on the heat pump’s seasonal performance.
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COP, SPF and SCOP: the numbers you should request
COP is a laboratory or operating-point result
The coefficient of performance (COP) compares heat output with electricity input at a particular outdoor temperature, water temperature and test condition. The IEA gives a typical household example with a COP of about four: four units of heat output for one unit of electricity. A COP can change substantially when outdoor air gets colder or the system has to produce hotter water.
SPF and SCOP describe a whole season
The seasonal performance factor (SPF) or seasonal coefficient of performance (SCOP) averages performance across heating operation, including changing outdoor temperatures and the system’s electricity consumption. It is the more useful figure for estimating annual energy use. Ask whether the installer’s forecast includes pumps, fans, controls, defrost cycles and any electric backup heater; otherwise the forecast may not match the electricity meter.
Energy Saving Trust cites a typical heat-pump SPF of 3.1 and says a well-installed, well-managed system can exceed 4. Its monitored trial reported average SPF values of 2.45 for air-source systems and 2.82 for ground-source systems. Those monitored averages are evidence of real operating performance, not a promise for every property.
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How seasonal performance changes in a real home
The same heat pump can use very different amounts of electricity in two houses. Seasonal performance falls when the heat pump must work at a high flow temperature, when the outdoor source is very cold, or when controls repeatedly start and stop the compressor.
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- Cold weather: An air-source unit has less readily available heat as outdoor temperature drops, and it may temporarily run a defrost cycle.
- High flow temperature: Supplying very hot water reduces the heat pump’s COP. Heat pumps generally work best with a steady, lower-temperature output.
- Small or unsuitable emitters: Existing radiators designed for a hot boiler circuit may not emit enough heat at a lower heat-pump flow temperature. Larger radiators, fan-assisted emitters or underfloor heating may be needed.
- Heat loss and draughts: A leaky building demands more heat and can force the system to run harder for longer.
- Controls: Poor weather compensation, incorrect room sensors or aggressive setbacks can reduce efficiency. Heat pumps usually prefer stable operation rather than large daily temperature swings.
- Auxiliary heat: An immersion heater or other backup element can consume electricity at an efficiency close to one unit of heat per unit of electricity, lowering the overall SPF if it runs frequently.
- Installation quality: Incorrect refrigerant charging, hydraulic balancing, pipe insulation or commissioning can reduce performance even when the equipment’s published rating is high.
Are heat pumps cheaper to run than gas boilers?
There is no universal answer without your tariffs and heat demand. Use the following relationship for a first estimate:
Heat-pump electricity cost per kWh of delivered heat = electricity tariff ÷ seasonal SPFBoiler gas cost per kWh of delivered heat = gas tariff ÷ boiler efficiency
The heat pump is cheaper on energy charges when:
electricity price ÷ gas price < SPF ÷ boiler efficiency
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The IEA tariff examples show why geography matters
| Country used in the IEA chart | Electricity price assumption | Gas price assumption | Electricity-to-gas ratio | Implication when comparing a heat pump with a gas boiler |
|---|---|---|---|---|
| United Kingdom | USD 0.31/kWh | USD 0.08/kWh | 3.875 | A high electricity price relative to gas can reduce or erase the heat pump’s running-cost advantage, depending on SPF and boiler efficiency. |
| France | USD 0.25/kWh | USD 0.11/kWh | About 2.27 | The lower price ratio is more favourable to heat-pump running costs. |
| Sweden | USD 0.23/kWh | USD 0.22/kWh | About 1.05 | Near-parity energy prices strongly favour the heat pump’s higher efficiency on the energy charge. |
The IEA values are assumptions used for comparison, not current offers for every household. Replace them with the unit rates on your own bills. If your electricity tariff has a cheap overnight period or a heat-pump-specific rate, calculate using the rate and operating schedule you can realistically obtain.
Do heat pumps work in poorly insulated homes?
Yes, but insulation and air-tightness still matter. The IEA says heat pumps work best in a well-insulated house because their heat output is at a lower temperature than a traditional boiler, and they perform best with a consistent heat output and minimal heat losses.
Insulation is not an absolute prerequisite. In an IEA 2024 UK model, replacing a 92% gas boiler with a high-efficiency heat pump cut heating energy use by 60–70% in an uninsulated, solid-walled house. That result shows that a heat pump can reduce delivered heating energy even in a difficult building, but it does not mean the occupants will automatically see the same percentage reduction on their bills. The model’s result depends on its climate, equipment assumptions, control strategy and energy prices.
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What to improve first
- Seal obvious draught paths around doors, windows and service penetrations while maintaining required ventilation.
- Insulate the loft or roof and hot-water pipework where practical.
- Assess wall and floor insulation for moisture, heritage and construction constraints before adding materials.
- Check windows and doors, but compare their heat-loss benefit with the cost of other measures.
- Have the installer recalculate room-by-room heat loss after major insulation work; reducing the load can change the required heat-pump size and radiator output.
Do not use a boiler’s existing capacity as a shortcut for sizing. A boiler may be substantially oversized, while a heat pump must be selected for the calculated design heat loss at the local design outdoor temperature.
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Heat-pump and gas-boiler differences beyond efficiency
| Decision factor | Heat pump | Gas boiler |
|---|---|---|
| Energy conversion | Moves ambient heat; seasonal efficiency can be several times its electricity input. | Burns gas; cited guidance places efficiency roughly between 75% and 92%, with about 85% typical for a new boiler. |
| Seasonal operation | Performance depends on source temperature, flow temperature, controls, emitters and commissioning. | Efficiency also varies with return temperature, cycling, boiler age and controls, but its output temperature is generally higher. |
| Upfront installation | Requires a heat-loss design, outdoor unit or ground loop, suitable emitters, electrical capacity, controls and hot-water planning. Obtain an itemized property-specific quote. | Usually involves the boiler, flue, gas connection, water circuit and controls. Replacement may be simpler where the existing system and radiators are retained. |
| Maintenance and servicing | Needs professional installation, commissioning and periodic checks of the refrigeration, electrical, hydraulic and control systems. | Needs qualified combustion and flue safety servicing and checks of the gas, condensate and heating circuits. |
| Cooling | Some reversible systems can provide cooling when designed and controlled for it; confirm that the selected model and emitters support this function. | A standard gas boiler provides heating and hot water, not active cooling. |
| Carbon impact | Depends on the electricity generation mix and the system’s seasonal electricity use. A cleaner grid lowers operating emissions. | Burns gas on site, so emissions are tied to fuel use as well as upstream supply. |
| Fuel-price exposure | More exposed to electricity prices, but uses fewer purchased energy units for the same heat. | Uses more fuel units per delivered kWh, with exposure to gas prices and boiler efficiency. |
A buyer’s checklist before you accept a quote
Ask installers to provide the following in writing. Comparing these details is more useful than comparing a single headline COP.
- Room-by-room heat-loss calculation: Request the heat loss for each room and the design outdoor temperature used. A whole-house estimate without room figures cannot verify radiator sizes.
- Design flow temperature: Ask for the flow temperature at the design condition and the expected return temperature. Lower temperatures generally support a higher COP.
- Emitter assessment: Have every radiator or underfloor circuit checked at the proposed flow temperature. Require a list of replacements or upgrades, not a general statement that existing radiators are adequate.
- Pipework and insulation review: Confirm that pipe diameters, circulation, buffer or volumiser arrangements and insulation match the design. Poor hydraulic design can increase pump electricity and reduce comfort.
- Predicted SPF or SCOP: Ask for the expected seasonal value and what it includes. Clarify whether domestic hot water, immersion-heater use, circulation pumps, fans and defrost electricity are counted.
- Tariff calculation: Supply your actual electricity and gas unit rates and ask for delivered-heat costs using those rates. Request separate figures for heating and hot water if the assumptions differ.
- Controls strategy: Identify the weather-compensation sensor, room controls, hot-water schedule and any setback temperatures. Ask how the system will be commissioned and tuned after the first heating season.
- Backup-heater plan: Find out when electric backup heat is allowed to operate, how it is limited and how faults are handled during very cold weather.
- Installer qualifications and handover: Verify relevant local certification, obtain commissioning records and keep the final design flow temperature, refrigerant information and control settings.
Use the phrase air-source heat pump to begin product research, not as a substitute for a heat-loss survey or code-compliant design. Equipment ratings from a catalogue do not predict the SPF of an installation that has not been sized for your rooms, emitters and climate.
Common mistakes that produce disappointing results
Choosing by nominal COP alone
A high COP measured at a mild outdoor temperature and low water temperature may not represent winter operation. Compare the manufacturer’s operating data at the flow temperature your radiators require and then ask for an installer’s seasonal SPF estimate.
Keeping boiler-style temperature setbacks
Turning a heat pump off for long periods and demanding a rapid recovery can trigger high flow temperatures or backup heat. Use the control strategy recommended for the specific system and have the installer explain the recovery limits.
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Ignoring domestic hot water
Hot-water production often requires a higher temperature than space heating. Ask how the cylinder is heated, how often an immersion cycle runs and whether the quoted SPF includes those kilowatt-hours.
Assuming insulation is all-or-nothing
A house does not need to reach a particular insulation standard before a heat pump can work. Instead, identify the practical measures that reduce heat loss, then resize emitters and recalculate the design load where the changes are substantial.
Comparing annual bills without matching assumptions
One quote may assume an SPF of 4, another 2.5; one may include hot water and standing charges, another may not. Put both systems on the same delivered-heat demand, tariff period, indoor temperature and scope of included costs before deciding.
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Bottom line for different household priorities
- Lowest delivered energy use: A correctly designed heat pump normally wins because it moves more heat per unit of purchased energy.
- Lowest immediate energy bill: Check your electricity-to-gas price ratio and the heat pump’s realistic SPF. Expensive electricity can offset its efficiency advantage.
- Older, draughty or uninsulated home: A heat pump can still reduce heating energy, as shown by the IEA’s 60–70% modeled saving in an uninsulated solid-walled UK example, but fabric improvements and emitter checks are especially important.
- Most reliable prediction: Use a room-by-room heat-loss calculation, a stated design flow temperature and a seasonal SPF estimate that includes all system electricity.
The right comparison is therefore not “heat pump or boiler” in the abstract. It is the cost and energy required to deliver the same heat in your particular home, under your local tariffs and with a documented design.
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