Heat Battery or Heat Pump?

If you are choosing between a heat battery and a heat pump, the honest starting point is that they are not quite the same kind of product. A heat battery stores heat, usually for hot water, and is most at home in smaller properties without space for outdoor equipment¹. A heat pump generates heating for the whole house and, in most UK homes, the realistic option is an air source heat pump: the most common type of domestic heat pump in the UK, suitable for most types of home², and officially assessed as technically suitable for most UK homes if installed appropriately³.

The money is also on a different scale. An air source heat pump typically costs £7,000 to £13,000 installed⁴, against a Boiler Upgrade Scheme grant of £7,500 for an air-to-water heat pump⁶, while heat batteries attract a £2,500 grant¹. A heat pump is the bigger project, but it is the one that takes a home off gas for both heating and hot water, which is the deeper prize for energy independence.

Quick verdict: most homes suit an air source heat pump

Air source heat pumps are the most common type of domestic heat pump in the UK and are suitable for most types of home². That is not just the view of one advice body: a parliamentary research briefing states that heat pumps are technically suitable for most UK homes if installed appropriately³. The two types most common in the UK are air source and ground source¹⁰, and ground source is the minority choice because it usually requires lots of outdoor space and higher installation costs than air source¹¹.

Where does that leave the heat battery? Heat batteries are most suitable for smaller homes that do not have space for an outdoor heat pump unit¹. So the practical dividing line is space and ambition. If the goal is to replace gas heating for the whole house and there is somewhere to put an outdoor unit, the air source heat pump is the mainstream route, with the installer base, the grant support and the planning framework built around it. If there is no outdoor space, or the aim is only to decarbonise hot water, a heat battery is the narrower but workable option, and you can read more in our comparison of heat battery vs hot water cylinder.

For independence, a heat pump takes the household off gas entirely: no gas boiler, no gas standing charge for heating, no exposure to gas price shocks. What remains is the electricity supply and the grid, because a heat pump runs on electricity and, on most tariffs, its running cost depends on the electricity price. A heat battery keeps the same dependence but adds a different one: it still needs an immersion heater or other input, and it covers hot water only.

Air source heat pumps transfer warmth rather than create it

An air source heat pump is a device that transfers heat from outside your home into your home using electricity, rather than generating the heat itself⁹. It works like a fridge in reverse: it absorbs heat from its source, the outside atmosphere, and transfers it at low temperature to the pump compressor⁹. Official planning guidance puts it plainly: an air source heat pump moves heat from the air to a hot water supply¹².

The crucial consequence is that the amount of heat produced by the system is more than the electricity needed to power it⁹. A resistive electric heater, including the element inside most heat batteries, turns one unit of electricity into at most one unit of heat. A heat pump uses its electricity to move heat that already exists in the outside air, so the same unit of electricity delivers several units of heat into your radiators or underfloor heating.

An air-to-water heat pump transfers heat drawn from the surrounding air to water in a wet central heating system⁹, which is why it can slot into an existing radiator circuit. It can also heat your water as well as your home⁹, which matters when comparing against a heat battery: the heat pump does both jobs, the heat battery does one.

Three to four times as efficient as a gas boiler

The headline efficiency claim is consistent across official sources. The Climate Change Committee says heat pumps are around three to four times more efficient than gas boilers, which should lead to lower household energy bills⁷. The UK government's clean energy campaign states heat pumps are three times more energy efficient than traditional boilers¹³, and the Welsh government says the same¹⁴. Bristol's council plan puts it as typically over three times more efficient than the most efficient gas boilers or electric heaters⁵, and official statistics note current heat pump technologies can be up to three to five times more efficient than a natural gas boiler⁴.

Against a heat battery, the comparison is stark. A heat battery charged by an immersion heater is limited by what electricity can do directly: one unit in, at most one unit of heat out. A heat pump delivers several units of heat per unit of electricity. That is the whole reason a heat pump can be cheaper to run than direct electric heating even though both run on electricity, and it is why the efficiency question, not the purchase price, is usually what decides the economics of this choice.

The efficiency is not fixed, however. Heat pumps are more efficient in well-insulated homes¹¹, and draughts or poor roof insulation can cause substantial heat loss and wasted energy¹¹. The system also has to be designed for the house: an undersized heat pump or one running radiators too cool will perform worse than the headline figures suggest. The efficiency advantage is real, but it is earned by the whole installation, not guaranteed by the box on the wall.

Cost: £7,000 to £13,000 installed, with £7,500 of Boiler Upgrade Scheme support

An air source heat pump typically costs £7,000 to £13,000 installed⁴. Other estimates differ: Energy Saving Trust estimates a typical cost of around £14,000¹¹, and independent advice puts an air-to-water heat pump at around £11,000 to install¹. The figures differ because they cover different mixes of property, system size and installation work, so treat the range as £7,000 to £14,000 depending on the house.

Against that, the Boiler Upgrade Scheme provides a grant of £7,500 for air-to-water heat pumps and ground source heat pumps⁶. Heat batteries are eligible for a £2,500 grant through the scheme¹, and the official scheme rules confirm the £2,500 value¹⁵. The government has also confirmed that a £2,500 grant for heat batteries will be available once the legislation and appropriate product standards are in place¹⁶, which is worth checking before any commitment, since the heat battery route depends on those standards being finalised.

Once the voucher is issued, it is valid for 3 months for an air-to-water heat pump and 6 months for a ground source heat pump¹⁷. Independent advice is to get quotes from at least three different installers to make sure of value for money², and Energy Saving Trust's heat pump fact-check repeats the same advice¹⁸.

Standard tariffs cost more than gas, time-of-use tariffs less

On standard electricity tariffs, where electricity is nearly four times more expensive than gas, heat pumps can cost slightly more to run than new gas or oil boilers². That is the uncomfortable truth at the heart of the running-cost debate, and it is why the tariff matters as much as the hardware.

The same research points the other way: by switching to a heat pump time-of-use tariff, you can reduce running costs significantly, and a heat pump can cost less to run than a gas boiler on such a tariff². Energy Saving Trust's in-depth guidance agrees that switching to a heat pump time-of-use tariff should reduce the cost of running the heat pump, making it more likely that you will save money¹⁹, and its fact-check adds that on a tariff charging different rates at different times of day, you could save money on your bills¹⁸.

For a heat battery, the time-of-use logic is the whole point: a heat battery charges when electricity is cheap and releases the heat when you need hot water. A heat pump on a smart time-of-use tariff does something similar, heating the house when power is cheap. The difference is that the heat pump's efficiency means each cheap unit of electricity delivers several units of heat, while the heat battery's stored heat costs one unit in for one unit out. Neither option frees a household from the electricity supplier: both depend on a tariff and on the grid's prices, and the running-cost case for either rests on shifting consumption to cheap hours.

The outdoor unit: space, noise and the 42 decibel limit

An air source heat pump needs an outdoor unit²⁰, and siting it is the main physical constraint. All parts of the air source heat pump must be at least one metre from the property boundary⁸, and the same one-metre limit appears in the legislation governing permitted development²¹. In Northern Ireland, the rules are stricter: no part of the air source heat pump may be less than 30 metres from a dwelling house other than your own²².

Noise is the other constraint. Noise levels for an air source heat pump on its own must stay at or below 42 decibels from a metre distance away from any habitable room⁸. In the UK, the legal noise limit for heat pumps is 42 decibels²³. For context, the typical range of a heat pump when it is on is between 40 and 60 decibels¹⁸, so the legal limit sits at the quiet end of what these machines produce, and manufacturers design their units to meet it.

Ground source heat pumps avoid the outdoor unit altogether: they do not need an outdoor unit, but they do need a large indoor unit²⁰, plus outside space for trenches or boreholes and enough room inside for the heat unit²³. A heat battery avoids both problems, which is exactly why heat batteries are most suitable for smaller homes that do not have space for an outdoor heat pump unit¹. If a home has no suitable exterior wall or garden, that constraint may decide the question before cost or efficiency come into it.

Installing without planning permission under permitted development

In general, planning permission is not needed to install a heat pump, because most heat pump installations are a permitted development¹⁹. Domestic heat pumps benefit from permitted development rights, which means in most cases planning permission is not required, subject to certain limitations and conditions²⁴. Permitted development rights allow air source heat pumps to be installed on detached houses or blocks of flats without planning permission¹².

The conditions matter. The permitted development rights cover the installation, alteration or replacement of an air source heat pump on a house or block of flats, or within its curtilage, including on a building within that curtilage²⁵. The volume of the outdoor compressor unit, including its housing, must not exceed 1.5 cubic metres on a house or 0.6 cubic metres on a block of flats²⁵. Only the first installation of an air source heat pump is permitted development on a house which is not detached or a block of flats; for detached houses, the first two are permitted²⁵. Development is permitted only if the installation complies with the Microgeneration Certification Scheme planning standards, MCS 020a²⁵.

• Ground and water source heat pumps on domestic premises are usually considered permitted development, not needing a planning application²⁶.
• An air source heat pump cannot be installed in a listed building or scheduled monument without planning permission²⁷.
• If the property is listed, listed building consent is usually needed before installing an air source heat pump, even where planning permission is not required²⁸.
• Ground source installation within the curtilage of a house or block of flats does not require planning permission, but listed building consent may be required if the property is listed²⁹.

A heat battery, sitting indoors, avoids nearly all of this: there is no outdoor unit, no boundary rule and no noise assessment. That simplicity is a genuine advantage, and for flats and terraced homes it can be decisive.

Homes where a heat pump works well, and where it may not pay

Heat pumps suit buildings with good insulation levels³⁰, and insulation may need to be added internally or externally if a home does not already have good levels³⁰. The warning from official guidance is direct: if your home is not well insulated, installing a heat pump may increase your energy bills instead, because electricity is more expensive than gas²³. That is the single biggest caveat on the whole heat pump case, and it is why the insulation state of the house should be settled before the heating choice.

The decision between air source and ground source comes down to space, budget and efficiency²⁰, and between a heat pump and a heat battery the same three factors apply, plus what the system is expected to do. A heat pump replaces the boiler: whole-house heating and hot water, off gas, with a £7,500 grant and a permitted development framework designed for it. A heat battery replaces the hot water cylinder's energy source: cheaper to install, simpler to site, £2,500 of grant support¹, but it leaves the heating system, and usually the gas boiler, exactly where it was.

For a household's energy independence, the heat pump is the bigger step and the bigger commitment. It removes the gas dependency but deepens the electricity dependency, and its economics depend on the tariff and on the fabric of the house. The heat battery is a smaller, safer move that leaves most of the household's energy dependence untouched. Neither is a wrong answer; they are answers to different questions, and the honest comparison starts by admitting that.