Heat Pump vs Gas Boiler: Running Costs and Efficiency
A heat pump is usually more efficient than a gas boiler, but whether it costs less to run depends on electricity and gas prices, the system’s real-world efficiency, and how well the home retains heat. Compare the cost of useful heat—not headline efficiency figures—and include installation, maintenance and any changes needed to radiators or insulation.
How heat pumps and gas boilers work
A gas boiler burns fuel to heat water, which circulates through radiators or underfloor heating. Its efficiency describes how much energy in the gas becomes useful heat; some energy is lost through the flue and during operation. Modern condensing boilers can recover some heat from exhaust gases, particularly when the return water is cool enough for condensing to occur.
An air-source or ground-source heat pump moves heat from outside air or the ground into the home using a refrigerant cycle and electricity. It does not turn each unit of electricity into only one unit of heat: it transfers existing heat as well. Its seasonal coefficient of performance (SCOP) expresses the heat delivered over a season divided by the electricity used. A SCOP of 3, for example, means roughly 3 kWh of heat per 1 kWh of electricity over the stated test or operating period. Actual performance varies with weather, system design and controls.
That is why the often-quoted comparison of a heat pump at “300% efficiency” with a boiler at about 90% can mislead. The figures describe different processes and do not by themselves tell you which system costs less. Price per unit of energy matters too.
How to compare running costs
Use the same amount of useful heat for both systems. A simple estimate is:
- Heat pump electricity used = useful heat required ÷ seasonal performance factor.
- Boiler gas used = useful heat required ÷ boiler seasonal efficiency.
- Running cost = energy used × the relevant price per unit.
For an illustrative calculation, suppose a home needs 12,000 kWh of useful heat in a year, the heat pump achieves a seasonal factor of 3, the boiler’s seasonal efficiency is 90%, electricity costs 30 pence per kWh and gas costs 7 pence per kWh. The heat pump would use about 4,000 kWh of electricity, costing £1,200. The boiler would use about 13,333 kWh of gas, costing about £933. Under those assumptions the boiler is cheaper to run, despite using more energy. These are example rates and assumptions, not a forecast or current tariff quote.
A useful break-even test is to compare electricity price divided by heat-pump seasonal performance with gas price divided by boiler efficiency. If the former is lower, the heat pump’s variable energy cost per unit of heat is lower. Include standing charges carefully: if replacing a boiler lets you close a gas account, the avoided gas standing charge can affect the household comparison. If gas remains for cooking or another appliance, that saving may not apply.
What changes real-world efficiency
Heat pumps generally perform best when they can deliver heat at relatively low water temperatures for long periods. Large or well-sized radiators, underfloor heating and a suitable flow-temperature setting can help. A high flow temperature makes the heat pump work harder and can reduce its seasonal performance. A badly sized unit, poor commissioning, unsuitable controls or frequent use of direct electric backup can also raise electricity consumption.
Outdoor conditions matter, especially for air-source systems. Efficiency can fall in cold weather, and the unit may periodically defrost. Ground-source systems draw from a steadier temperature source but usually involve more extensive groundwork. For boilers, seasonal efficiency is affected by system condition, boiler sizing, controls, water temperature and whether the appliance can operate in condensing mode for much of the time.
Insulation and draught reduction lower the amount of heat a home needs, reducing running costs for either system. They may also make it easier to heat a home with lower water temperatures, which can improve heat-pump performance. Ask for an assessment of room-by-room heat loss rather than assuming that replacing the boiler with a heat pump is a like-for-like swap.
Installation costs and home suitability
Running costs are only part of the decision. Compare the total cost over the period you expect to stay in the property, including equipment, installation, required electrical work, maintenance and likely replacements. Heat pumps can require an outdoor unit, space for a hot-water cylinder, changes to pipework or radiators, and a suitable electrical supply. Ground-source installation adds the cost and disruption of ground loops or boreholes. A gas boiler may be simpler to replace where an existing gas connection and compatible system are already present.
Before choosing, check:
- A heat-loss calculation and the proposed heat pump’s output at relevant outdoor and water temperatures.
- Whether existing radiators can deliver enough heat at the system’s planned flow temperature; some may need replacing or enlarging.
- Where the outdoor unit can go, including airflow, access, drainage and potential noise considerations.
- Hot-water cylinder space, electrical capacity, controls and any planned insulation improvements.
- Written estimates that separate equipment, installation, remedial work and ongoing service requirements.
Installation quality is crucial. Ask the installer to explain the design assumptions, expected seasonal performance, commissioning and how the controls should be used. A quoted performance figure is not a guarantee of your actual bills.
Comfort, maintenance and common misconceptions
A heat pump can feel different from a boiler because it often runs for longer at a lower flow temperature instead of heating radiators quickly to a high temperature. That does not mean it cannot keep a home warm; it means the system must be designed and controlled for the building. Turning the thermostat down substantially overnight and expecting a rapid recovery may not suit every setup. Follow the system designer’s guidance and judge comfort over normal operating conditions.
Neither option is maintenance-free. Boilers need appropriate servicing and checks; heat pumps also need inspection and upkeep according to the manufacturer and installer’s instructions. Keep the outdoor heat-pump unit clear of leaves, snow and other airflow obstructions, without interfering with its components. Do not attempt repairs on gas, refrigerant or electrical equipment yourself; use appropriately qualified professionals.
Another misconception is that a heat pump always produces cheaper heat because its efficiency is higher. It may use far less purchased energy, yet still cost more when electricity is expensive relative to gas or when the system performs poorly. Conversely, a well-designed heat pump on a favourable electricity tariff can be competitive. Compare measured or realistically modelled seasonal performance and your actual tariffs.
Frequently Asked Questions
Is a heat pump cheaper to run than a gas boiler?
Not in every home. It depends mainly on the electricity-to-gas price ratio, the heat pump’s seasonal performance and the boiler’s seasonal efficiency. Compare cost per unit of useful heat using your current tariffs.
What does a heat pump COP of 3 mean?
It means the system delivered about three units of heat for each unit of electricity used over the period measured. Seasonal performance is more useful for estimating annual bills than a single operating-condition COP.
Can I keep my existing radiators with a heat pump?
Possibly. A heat-loss and radiator-output assessment is needed to confirm whether they can keep rooms warm at the heat pump’s planned water temperature. Some radiators may need to be enlarged or replaced.
Do heat pumps work in cold weather?
Air-source heat pumps can operate in cold weather, although performance and available output can change as outdoor temperatures fall. The system must be correctly sized for local conditions and the home’s heat demand.
Should I improve insulation before installing a heat pump?
Reducing heat loss can lower bills and may allow a smaller system or lower operating temperatures. An assessment can help identify worthwhile improvements, but the right sequence depends on the building and project.
Which costs should I compare besides fuel?
Include installation and any radiator, cylinder, electrical or building work, plus maintenance and possible changes to standing charges. Consider grants or incentives only after checking current eligibility and terms from the relevant official source.
Related
Method: the standard formula for this calculation, rounded as each result states. See how the calculators work or report an error.