Heat Pumps – Frequently Asked Questions

A heat pump moves heat rather than generating it from a fuel. It extracts low-grade heat from the air, ground, or water outside, uses a refrigerant cycle and an electrically driven compressor to raise that heat to a usable temperature, and delivers it into your home's heating and hot water system. Because it's moving heat rather than burning fuel to create it, a well-installed heat pump typically produces two-and-a-half to four times more heat energy than the electrical energy it consumes.

• Air source heat pumps (ASHP): the most common type in UK homes. They extract heat from outdoor air and are relatively straightforward to install, usually sitting on a slab or wall bracket outside. Most of our air source heat pump range falls here.
• Ground source heat pumps (GSHP): use buried pipework (horizontal trenches or vertical boreholes) to draw more stable heat from the ground. Higher upfront cost and more disruptive to install, but often steadier efficiency through winter.
• Water source heat pumps: draw heat from a nearby pond, lake, or borehole water source. Efficient where the site allows it, but only relevant to a small number of UK properties.

For most retrofit projects in the UK, an air source heat pump is the practical starting point — our buying guide covers how to choose between brands and models.

Yes. Modern air source heat pumps are designed and tested to operate efficiently down to outdoor temperatures well below what most of the UK experiences, including sub-zero conditions. Efficiency does fall gradually as it gets colder outside — the unit works harder to lift heat from colder air — but properly sized systems from major brands are rated for UK winters and are already widely installed from Cornwall to the Scottish Highlands.

It depends on what you're replacing and how well the system is sized. Heat pumps typically deliver three to four units of heat for every unit of electricity used, so compared with an old gas boiler or direct electric heating, most well-installed systems bring a genuine reduction in heating costs. Replacing oil or LPG usually shows the biggest saving, since those fuels cost more per kWh than mains gas. The size of the saving depends on your current tariff, whether you're on a heat-pump-friendly electricity rate, and how well insulated the property is — a poorly insulated home will see a smaller saving until draughtproofing and insulation are addressed too.

COP (Coefficient of Performance) is a snapshot efficiency figure measured under one specific set of conditions — for example, at a given outdoor and flow temperature. A COP of 3.5 means the unit delivers 3.5 kW of heat for every 1 kW of electricity it consumes at that moment.

SCOP (Seasonal Coefficient of Performance) is more useful for comparing running costs, because it averages efficiency across a full heating season, including cold snaps and mild spells. When comparing models or brands, always check SCOP rather than a single COP figure quoted at ideal conditions — it's a far better guide to what you'll actually pay over a winter.

Efficiency drops as outdoor temperature falls, because the unit has to work harder to extract heat from colder air — but a correctly sized heat pump should still comfortably heat the home. Most modern units include a backup immersion heater in the cylinder or an integral electric element for the rare occasions temperatures fall outside the design range, and many can also run a defrost cycle automatically to clear frost from the outdoor unit without you needing to intervene.

Heat pumps are especially well matched to underfloor heating because it operates at low flow temperatures, which is exactly where a heat pump is most efficient. They also work well with radiators, provided the radiators are sized correctly for lower flow temperatures than a gas boiler typically runs at — often this means upsizing some radiators during installation rather than replacing the whole system. A proper heat loss survey, covered in our buying guide, tells you exactly which rooms need attention.

Not necessarily all of them. A heat loss calculation is done room by room, and typically only the radiators that are undersized for the lower flow temperature are swapped for larger units or double panels — the rest can often stay as they are. In some cases, adding thermostatic radiator valves and rebalancing the system delivers most of the benefit without full replacement.

Yes — almost all heat pump systems need a hot water cylinder, since heat pumps can't provide the instant, high-temperature hot water that a combi boiler does. If you currently have a combi boiler with no cylinder, space for one (often in an airing cupboard or utility room) needs to be factored into the installation. Browse our heat pump cylinders and pre-plumbed cylinder ranges to see typical sizes.

They can, but siting the outdoor unit is the main constraint. Flats without private outdoor space, or terraces with very tight side access, sometimes struggle to accommodate a standard outdoor unit and its required clearances. Compact and low-noise models exist specifically for these situations, and in blocks of flats a communal or air-to-air system is sometimes more practical than an individual air-to-water unit. It's worth a site-specific chat with our team before assuming either way.

Most modern air source heat pumps run at around 40–60 decibels at one metre, depending on the model and how hard it's working — comparable to a quiet conversation or light rainfall, and quieter than most external air conditioning condensers. Noise output typically rises briefly during defrost cycles or in very cold weather when the compressor works harder. Correct siting — away from bedroom windows and with adequate clearance from walls and fences — makes a bigger practical difference than the manufacturer's decibel rating alone.

Most air source heat pump installations on houses in England and Wales fall under permitted development and don't need planning permission, provided the unit meets standard size, distance-from-boundary, and noise (MCS Planning Standard) criteria. You're more likely to need permission for listed buildings, conservation areas, flats and maisonettes, or larger/ground source installations. Rules differ slightly in Scotland and Northern Ireland, so always check with your local planning authority before ordering equipment if your property is in any of these categories.

The Boiler Upgrade Scheme (BUS) is the main UK government grant for heat pump installation in England and Wales. Current grant levels:

See our dedicated UK energy subsidies and grants FAQ for full eligibility criteria and how the off-gas-grid uplift works, and confirm current figures with your installer or on GOV.UK before budgeting, as scheme terms are periodically revised.

A straightforward air source heat pump retrofit — new outdoor unit, cylinder, and any radiator upgrades — typically takes two to four days once the heat loss survey and equipment order are done. Ground source systems take considerably longer because of the groundworks or borehole drilling involved, often one to two weeks. Lead time before installation (surveying, ordering equipment, scheduling an MCS-certified installer) usually adds several weeks on top of the on-site work itself.

Sizing should come from a room-by-room heat loss calculation, not a rule of thumb based on house size or previous boiler rating — an oversized heat pump cycles inefficiently, and an undersized one struggles on the coldest days. Our heat pump sizing calculator gives a starting estimate based on your property, and any installer quoting you should carry out a full survey before confirming the final kW rating.

Heat pumps need less routine maintenance than a gas boiler. In practice this means keeping the outdoor unit's air intake clear of leaves and debris, an occasional filter or strainer check, and one professional service a year to check refrigerant pressures, electrical connections, and system performance — similar in scope to an annual boiler service.

No — not if you want to claim the Boiler Upgrade Scheme grant or keep the manufacturer's warranty valid. Installation involves refrigerant handling (which legally requires F-Gas certification), electrical work, and system commissioning that needs to be signed off by an MCS-certified installer. DIY installation of the associated pipework or a compatible cylinder is sometimes feasible for competent tradespeople, but the heat pump itself should always go through a certified installer.

R32 and R290 (propane) are the two refrigerants most commonly used in current heat pump ranges. R32 has a lower global warming potential than older refrigerants and is well established, widely serviced, and used across most mainstream models. R290 has an even lower environmental impact and, being a natural refrigerant, typically supports higher flow temperatures — useful where you're keeping older, higher-temperature radiators — but it's mildly flammable, which affects installation siting rules and slightly limits where units can be placed. Both are safe, well-regulated choices when installed correctly; which one suits your project usually comes down to the specific brand and model rather than refrigerant type alone. Our Panasonic Aquarea R32 vs R290 guide and Mitsubishi Ecodan guide go into the model-specific detail.

Some heat pumps are reversible and can provide a limited amount of cooling in summer, usually through an underfloor heating loop or fan coil units rather than radiators (radiators aren't designed to run cold without condensation issues). Not every model or every installed system supports this — it depends on the heat pump's specification and how the rest of the heating system was designed. If summer cooling matters to you, flag it before you buy so the installer selects a model and configuration that supports it.

A well-installed and properly maintained air source heat pump typically lasts around 15–20 years, broadly comparable to or longer than a gas boiler's working life, with the compressor as the main wear component. Most manufacturers offer warranties of 2–7 years as standard, with extended cover available on many models when installed and registered by an accredited installer — worth checking model by model before you buy.