Are Heat Pumps Too Big for UK Homes? Real Unit Sizes Explained

"Where would I even put it?" It is one of the most common objections to heat pumps in the UK, and it is entirely understandable. If your mental image of a heat pump is an industrial-looking box the size of a car, then of course it would not fit in the average UK garden. But that image is wrong. Modern air source heat pumps are compact, quiet, and designed specifically for the kinds of properties that make up the UK housing stock.

This guide sets out the real dimensions of popular models, taken from manufacturer specifications, and the placement options installers commonly use across UK property types — Victorian terraces, 1930s semis, post-war houses, modern townhouses and flats. For most homes, size is a smaller obstacle than people expect, though every property needs its own survey.

How Big Is a Heat Pump, Really?

Let us start with actual dimensions. Here are the physical sizes of popular UK heat pump models:

Dimensions from manufacturer technical specifications. All models currently available in the UK market.

The Mitsubishi Ecodan 8.5kW, for example, is just 800mm x 300mm x 713mm — roughly the size of a bedside table. Even the larger units are comparable to a small chest freezer. These are not the industrial monstrosities that some people imagine.

Size Comparison: Every Major Brand

For a full comparison of physical dimensions across all UK brands and sizes, see our dedicated size comparison guide. The key takeaway: all major brands offer compact units suitable for UK homes, and the trend is towards even smaller designs with each new generation.

Terraced Houses

Terraced houses present the biggest perceived challenge due to narrow side access and small rear gardens. The usual options are:

• In the rear garden or yard against the back wall, with the unit carried through the house during installation
• In the side passage, where one exists
• On a wall-mounted bracket on the rear wall, elevated off the ground

Placing the unit against the rear wall of the house, near the kitchen, is often the simplest choice. This keeps pipework runs short (reducing cost and heat loss) and places the unit where noise impact on neighbours is minimised. Even in a garden only 3-4 metres deep, a typical unit occupies less than 1 square metre — leaving the vast majority of garden space unaffected.

Semi-Detached Houses

Semi-detached houses typically have side access and a larger rear garden, making placement straightforward. Common options are:

• On the side passage or driveway
• In the rear garden, against the house wall
• On a concrete pad at the side of the rear garden

Side passage placement often suits semis because it keeps the unit out of the main garden, close to the house for short pipework, and away from bedroom windows. A side passage typically only needs to be 800mm wide for a heat pump installation.

Detached Homes

Detached homes generally have the most placement flexibility, with units usually placed at the side or rear of the property. In England a detached house may have up to two air source units under permitted development. The main consideration for detached homes is distance from neighbours — and with boundary distances typically greater than terraces or semis, noise is rarely a concern.

Urban and Compact Properties

Truly compact urban properties need more thought, but there are usually options. Typical approaches include:

• A ground-floor flat with the unit on a small patio area
• A townhouse with the unit in a small rear yard
• An end-terrace with the unit in a narrow side alley
• A wall-mounted unit on an external wall where ground space is limited

Many homeowners assume a heat pump will not fit before a survey shows that it can. Experienced installers can usually find a placement that is practical, compliant with regulations and acceptable to look at, but some properties genuinely lack a suitable spot, so get a site survey before you decide.

The Indoor Cylinder Question

The outdoor unit is only half the story. Inside, you need a hot water cylinder — typically 200-250 litres, measuring approximately 1,400-1,700mm tall by 550-600mm diameter. If you currently have a combi boiler (no cylinder), finding space for a cylinder is a genuine consideration.

Common cylinder locations include:

• Airing cupboard: If your home previously had a cylinder, the space likely still exists
• Utility room: Ideal if you have one
• Garage: Works well with proper insulation around the cylinder
• Under stairs: Many cupboards under stairs can accommodate a cylinder
• Corner of a room: Can be boxed in neatly with a timber surround

Homes that already have a system or regular boiler usually have cylinder space. Combi boiler homes typically find space in a utility room, garage, repurposed airing cupboard, under the stairs or a boxed-in corner of a room.

Creative Placement Solutions

Some creative solutions homeowners often have not considered:

Acoustic fencing: A small acoustic fence panel between the heat pump and the neighbour's garden can reduce noise towards the neighbour while also screening the unit visually.

Garden storage integration: A heat pump can sit beside or within a modified garden storage unit, provided the manufacturer's airflow clearances are kept, so it blends into the garden.

Elevated mounting: Wall brackets can lift the unit off the ground, freeing up ground space entirely. This approach works particularly well for properties with limited ground area or flood risk.

The key message: if you think a heat pump will not fit your property, it is worth checking before ruling it out. An experienced installer who has dealt with similar properties can tell you what is possible after a site survey.

Frequently Asked Questions

How big is a typical heat pump?

Approximately 800-1,100mm wide, 400-600mm deep, 700-900mm tall — roughly the size of a large suitcase or small washing machine. Newer compact models are even smaller.

Can I fit one in a small garden?

Yes. A heat pump needs about 1m² of ground space plus airflow clearance. Even very small gardens, side passages, and rear yards can accommodate one.

Can heat pumps go on roofs or walls?

Yes. Wall-mounted and flat-roof installations are increasingly common, especially in urban settings. Structural assessment may be needed.

What about the indoor cylinder?

A 200-250 litre cylinder (1,400-1,700mm tall, 550-600mm diameter) can go in airing cupboards, utility rooms, garages, or under stairs. If you had a cylinder before, the space likely still exists.

Are heat pumps getting smaller?

Yes. R290 refrigerant and improved compressor technology mean each generation is more compact. The trend is firmly towards smaller units.

Do I need planning permission?

Most installations in England fall under permitted development. The unit must meet the MCS noise standard and can be up to 1.5 cubic metres; the old 1 metre boundary rule was removed on 29 May 2025. Wales and Scotland have their own rules, so check with your local planning authority there. Conservation areas may have additional requirements.