As the UK pushes towards net zero, air source heat pumps have been positioned by government and industry as the frontrunner technology for decarbonising home heating. But is this reputation deserved, or is the picture more nuanced? To answer that, it helps to work through the practical questions homeowners and installers actually face.
Are heat pumps the best technology for low-cost heating in UK homes?
Not automatically. A heat pump’s running cost depends on its coefficient of performance (CoP) — typically 2.5 to 4, meaning it delivers two-and-a-half to four units of heat for every unit of electricity consumed — set against the price of electricity relative to gas. In the UK, electricity has historically cost around three to four times more per kWh than gas. This means a heat pump only becomes cheaper to run than a gas boiler once its CoP comfortably exceeds that price ratio. In a well-designed system this is achievable, but in a poorly optimised one, running costs can end up higher than a gas boiler, even though carbon emissions are lower. So heat pumps are a strong technology for low ‘carbon’ heating; whether they are the lowest cost option depends heavily on setup and electricity pricing.
What is the optimal set-up to get the best out of heat pumps?
To maximise CoP and therefore minimise running costs, a heat pump installation should include:
- Low flow temperatures (ideally 35–45°C rather than the 70–80°C boilers typically run at), since efficiency drops sharply as flow temperature rises
- Oversized radiators or underfloor heating, which can deliver comfortable heat at these lower temperatures
- Good building fabric insulation, reducing the heat output required in the first place
- A well-sized buffer or thermal store, avoiding excessive cycling
- Weather compensation controls, which modulate flow temperature to match outdoor conditions rather than running at a fixed high setpoint
- Correctly sized system design (via a proper heat loss survey), avoiding oversizing or undersizing the unit
Get these wrong and the heat pump will run at a higher flow temperature to compensate, sacrificing much of its efficiency advantage.
When is it better to use efficient condensing boilers?
Condensing boilers remain the more practical choice where:
- The building has poor insulation or limited scope for upgrades, and cannot support low-temperature heat emitters without expensive fabric works
- Radiators cannot be replaced or resized (e.g. rented or listed properties)
- There is no suitable outdoor space, or the property is a flat with restricted external wall access
- Electricity prices remain very high relative to gas, making running costs prohibitive
- A quick, low-disruption replacement is needed, and a full retrofit isn’t feasible in the short term
In these cases, a modern condensing boiler (90%+ efficiency) offers a sensible, lower-cost bridge, especially for older or hard-to-treat housing stock.
What are the best buildings in which to install and use heat pumps?
Heat pumps perform best in:
- New-build homes, designed from the outset with high insulation standards and underfloor heating
- Well-insulated existing homes, particularly detached or semi-detached properties with loft, wall, and floor insulation already in place
- Properties with outdoor space for siting the outdoor unit with adequate airflow
- Homes undergoing wider retrofit, where insulation upgrades are happening anyway, making heat pump installation part of a holistic energy improvement
They are less suited, at least without significant preparatory work, to solid-wall Victorian terraces, high-rise flats, and homes with limited insulation or space constraints.
If hydrogen eventually becomes the fuel of choice, what technology should we use in the meantime?
Hydrogen for domestic heating remains unproven at scale in the UK, with ongoing trials but no confirmed national rollout timeline, and significant questions remain around production costs, distribution infrastructure, and overall efficiency. In the interim, the most sensible approach is to install technology that delivers immediate carbon reductions without foreclosing future options. Air source heat pumps fit this role well: they cut emissions now, using proven and scalable technology, while the electricity grid itself continues to decarbonise, compounding the carbon savings over time. Where hydrogen-ready boilers are fitted as an interim step, they should be treated as a bridging measure rather than a long-term low carbon solution, since the wider hydrogen heating infrastructure is not yet in place.
How can the benefits of a heat pump versus a condensing boiler be continuously assessed?
Ongoing comparison should track:
- Actual metered CoP, using in-situ monitoring (many modern heat pumps report this via an app or smart meter integration), compared against manufacturer specifications
- Running costs per kWh of heat delivered, recalculated as electricity and gas tariffs shift
- Carbon emissions per kWh of heat delivered, using the current grid carbon intensity factor, which is falling year on year as renewable generation increases
- System performance against the original design assumption, flagging if flow temperatures are creeping up or efficiency is degrading
This kind of ongoing monitoring, rather than a one-off installation assessment, is what reveals whether a heat pump is genuinely outperforming a boiler in a given home.
Conclusion: So, are heat pumps the holy grail?
Air source heat pumps are not a universal silver bullet, but for the right building, with the right design, they are currently the most effective proven technology for decarbonising home heating in the UK. Their advantage is not guaranteed by installation alone; it depends on getting the fundamentals right — low flow temperatures, adequate insulation, correctly sized emitters and controls. The efficacy of the wide scale use of heat pumps is directly related to both the price and emissions factor of electricity compared to gas. The UK government and energy industry need to work on reducing the cost of electricity if the advantages of heat pumps will be realised. Until that rebalancing happens, heat pumps will remain a genuinely powerful tool for low carbon heating, but not yet the unqualified “holy grail” the label suggests — and condensing boilers will continue to have a legitimate role in homes not yet ready for the transition.
If you are planning to retrofit an air source heat pump in your home, you should seek the service of an installer from the Microgeneration Scheme (MCS) from here:
Please reviewed all the resources on the MCS website to enhance your knowledge about heat pumps and other technologies the scheme supports.