The heat pump conversation in Britain has a bad habit of starting in the wrong place. People ask which type is best before anyone has established how much heat the house actually loses. When you compare air source vs ground source heat pump options honestly, the choice is decided far more by your building, your land and your radiators than by the units themselves.
For most UK homes, an air source heat pump is the realistic choice, a ground source system is better but only makes sense where there is land and a long horizon, and a hybrid is a compromise that suits hard-to-treat properties rather than a first preference. The rest of this piece is about how you work out which of those describes you.
The three options in one paragraph each
Air source
A unit outside the house extracts heat from outdoor air and transfers it to your heating and hot water. It needs a sensible outdoor position with airflow, a condensate drain, and space indoors for a hot water cylinder. Installation is measured in days. It is the default for a reason: it is the cheapest to install, the fastest to fit, and it works in British winters, albeit less efficiently as outdoor temperatures fall.
Ground source
Pipework buried in the ground - either horizontal trenches across a large area or vertical boreholes - extracts heat from a source that stays at a stable temperature all year. Because the source is stable, efficiency is higher and more consistent than air source, particularly in the coldest weeks when you need it most. It also costs substantially more, needs either significant land or drilling rigs on site, and turns your garden into a building site for a period.
Hybrid
A heat pump paired with a boiler, with controls deciding which runs. The heat pump handles the bulk of the year efficiently, and the boiler covers the coldest days and, in some configurations, hot water. It reduces the need to upgrade every radiator and avoids the worst-case sizing problem, at the cost of retaining a gas appliance, its servicing, and a more complicated system. Grant eligibility for hybrid arrangements is not the same as for a full heat pump, so check before assuming.
The comparison that matters
Installed cost
Indicative and highly dependent on property, before any grant:
Air source - commonly around £8,000 to £14,000 installed for a typical house, before grant support, and more where significant emitter upgrades or a new cylinder are needed.
Ground source - commonly £18,000 to £35,000 or more, with boreholes at the upper end and horizontal trenches cheaper where land allows.
Hybrid - varies enormously depending on whether the existing boiler stays, but usually sits between a boiler replacement and a full air source install.
Grant support materially changes these numbers for eligible properties, and the grant is normally applied for by the installer rather than the homeowner. Confirm current eligibility and amounts before budgeting.
Efficiency
Efficiency is expressed as SCOP - seasonal coefficient of performance, the average units of heat delivered per unit of electricity across a year. Higher is better.
Ground source generally achieves a higher SCOP than air source, because its heat source does not drop to freezing in February. But the single largest influence on real-world SCOP is the flow temperature the system runs at, and that is determined by how large your radiators are relative to the heat each room loses. A well-designed air source system running at a low flow temperature will outperform a badly designed ground source system running hot. Design beats technology.
Space and disruption
Air source - an outdoor unit roughly the size of a large fridge lying down, plus indoor cylinder space. A few days’ work.
Ground source - either a trench field needing a substantial area of accessible garden, or boreholes needing rig access. Plus plant space indoors. Weeks, and a garden that needs reinstating.
Hybrid - the boiler stays where it is, plus an outdoor unit. The least disruptive of the three.
Noise and planning
Air source units make noise, and the position relative to your own bedroom windows and your neighbours’ matters. Permitted development rights cover many domestic air source installations in England subject to conditions including siting and noise assessment, with different rules in the devolved nations and additional restrictions for listed buildings and conservation areas. Ground source plant is indoors and quiet, which in a tight terrace is a real advantage. Confirm the planning position for your property before committing.
Lifespan and maintenance
Heat pumps generally have a longer expected life than a gas boiler, and ground loops longer still - the buried pipework is usually expected to outlast the heat pump it feeds. All need annual servicing, and any system containing refrigerant has its own requirements. Budget for servicing exactly as you would for a boiler.
The part that decides it: your house, not the pump
The uncomfortable truth is that the heat pump is the least interesting decision in the project. What determines whether you end up warm and satisfied or cold and resentful is a proper room-by-room heat loss calculation, emitters sized for a low flow temperature, adequate insulation, and a system commissioned and balanced properly. Every failed installation you read about in the press is a design failure or a sizing failure, and hardly any are a failure of the technology.
So before you compare units:
Get a room-by-room heat loss survey. Not a rule of thumb per square metre, not a figure from the boiler size. An actual calculation.
Do the cheap fabric work first. Loft insulation, draught proofing and cylinder insulation are far cheaper per kilowatt saved than upsizing a heat pump. A smaller, well-designed system in a better-insulated house is the cheaper and better outcome.
Expect emitter changes. Many radiators sized for a 70-degree boiler flow are too small for a 45-degree heat pump flow. Underfloor heating is ideal. Larger or higher-output radiators in a few key rooms is common and normal.
Check the electrical supply. Your consumer unit and incoming supply need to accommodate the new load.
Check the cylinder. Most heat pump installs need a new, correctly sized cylinder with an adequate coil. Combi-only houses need to find space for one, and that is sometimes the real constraint.
Running costs, honestly
A heat pump uses electricity, which per unit costs considerably more than gas in the UK. Whether your bills fall depends on the ratio between those unit prices and the SCOP the system actually achieves. At a high SCOP the heat pump wins comfortably; at a poor SCOP, in a house with undersized emitters running a high flow temperature, the numbers can be uncomfortable.
This is why design matters financially and not just technically. It is also why any installer who quotes you a saving figure without having done a heat loss calculation is guessing.
Specialist heat pump electricity tariffs exist and can change the arithmetic meaningfully. Ask about them before you sign, and factor in the removal of gas standing charges if you are leaving gas entirely.
Choosing an installer
MCS certification matters, both for the standard of installation and because grant eligibility normally depends on it.
Ask to see the heat loss calculation and the emitter schedule. If they will not produce one, that is the end of the conversation.
Ask what flow temperature the system is designed to run at. A low design flow temperature is the single best indicator of a competent design.
Ask about noise assessment and where exactly the unit will sit.
Ask what happens at commissioning and what documentation you receive.
Get at least three quotes and compare the designs, not just the prices - they will not be quoting for the same thing.
Ask about the warranty on the unit, the installation and the workmanship, and who honours each.
What to do in the next 30 minutes
Find your latest EPC and note the recorded wall, roof and floor insulation.
Measure your loft insulation depth.
Photograph your existing radiators with a tape measure across them, and note which rooms are always cold.
Find out where a hot water cylinder could physically go.
Photograph the outside space where a unit could sit, and the nearest neighbouring window.
Check the current grant scheme in your nation and whether your property is eligible.
A heat pump project generates paperwork you will need for years - the heat loss survey, the MCS certificate, the commissioning sheet, the grant documentation, the warranty terms. It is also exactly what a buyer’s surveyor will ask for. Home+ gives you a free place to keep all of it against the system, with servicing reminders set from the commissioning date. When you are ready to gather quotes, compare installer quotes through Trade Pilot and keep the designs side by side.
FAQ
Is a ground source heat pump better than an air source? Technically yes - efficiency is higher and more stable because the ground temperature does not drop in winter. Practically it is only the better choice where you have sufficient land or borehole access, a budget two or three times higher, and the appetite for weeks of groundwork.
Will a heat pump work in an old British house? Yes, provided the heat loss is calculated properly and the emitters are sized for the flow temperature. Older, less insulated houses need more radiator upgrades and a larger unit, which costs more. The limiting factor is design and budget, not age.
Do I need to replace all my radiators? Usually not all of them. A proper survey identifies which rooms need larger emitters at the design flow temperature. In many houses it is a handful of rooms rather than the whole house.
Is a hybrid heat pump a good compromise? It suits hard-to-treat properties, homes where emitter upgrades are impractical, and people who want to reduce gas use without a full retrofit. The trade-offs are keeping a gas appliance, servicing two systems, and different grant treatment.
How noisy is an air source heat pump? Modern units are relatively quiet, but they are not silent and they run for long periods. Siting is what determines whether it is a non-issue or an annoyance. Ask for the noise assessment and stand next to a running unit before you commit.
Will a heat pump improve my EPC rating? Usually yes, particularly when replacing an older or non-condensing boiler, but the scale of improvement depends on the model’s treatment of the system and your fabric. Do not install one primarily for the certificate.
What grants are available? Grant support for heat pumps exists in the UK, applied for by the installer rather than the homeowner, with different schemes across the nations and eligibility conditions attached. Check the current position on gov.uk or with your devolved administration before budgeting, because amounts and rules change.
