The best place for a heat pump is usually on firm, level ground beside a side or rear wall, with open air around it, well away from neighbours’ windows and as close as possible to where the pipes enter the house. The exact spot is decided by airflow clearances, noise, planning rules, drainage and how far the pipes have to run.
This guide covers where the outdoor unit should go, where the indoor parts fit, how monobloc and split systems differ, and what to do if you live in a flat, a terrace or a home with a small garden.
What Clearances Does a Heat Pump Outdoor Unit Need?
Most air source heat pumps need about 250–300 mm behind the unit and 500–600 mm or more in front of the fan, plus room at the sides and top for airflow and servicing. The exact figures come from the manufacturer’s installation manual and differ between models.
| Model (installation manual) | Behind unit | In front of fan | Sides | Above |
|---|---|---|---|---|
| Grant Aerona 290 | 250 mm | 500 mm | 100 mm | 600 mm (1,000 mm on 12 and 15.5 kW) |
| Grant Aerona³ R32 | 300 mm | 600 mm | 100 mm left, 600 mm right | 300 mm |
Vaillant’s aroTHERM plus manual lists clearances between 100 mm and 1,000 mm depending on the side, with slightly more space needed when the unit also cools. These are minimums. An engineer needs to reach the service panels, and a unit squeezed into its minimum space is harder to maintain. Daikin’s Altherma 3 R manual also limits the height of any wall on the outlet side to 1,200 mm, so the discharged air can escape rather than bounce back.
In snowy areas, keep the unit clear of drifting snow. Daikin asks for at least 150 mm of free space below the unit, or 300 mm where heavy snowfall is common, and for the unit to sit at least 100 mm above the expected snow level.
How Close Can a Heat Pump Be to a Neighbour’s Window?
There is no fixed distance, but for permitted development in England the calculated noise level must be no more than 37 dB(A) at 1 metre from the centre of any neighbour’s habitable room window or door. The calculation follows MCS 020(a), which became mandatory for permitted development on 20 September 2025.
The MCS 020(a) method starts with the unit’s published sound power level. Low-noise mode cannot be used. It then adjusts for distance, for reflecting surfaces near the unit (the Q factor) and for any solid barrier between the unit and the window.
| MCS 020(a) factor | Condition | Effect |
|---|---|---|
| Q2 | One reflecting surface within 1 m | Lowest reflection penalty |
| Q4 | Two reflecting surfaces, such as ground and a wall | Typical ground-mounted unit against a house wall |
| Q8 | Three reflecting surfaces, such as a corner | Highest penalty; more than three surfaces will not comply |
| Type 1 barrier | Solid masonry or 18 mm+ solid barrier, no line of sight | Up to −10 dB |
| Type 2 barrier | Solid fence under 18 mm, no line of sight | Up to −5 dB |
To show how distance and position interact, the table below applies the MCS 020(a) formula to an illustrative heat pump with a sound power level of 58 dB(A) and no barrier. Your installer will use the actual model’s data and measured distances.
| Distance to neighbour’s window | Q2 (one surface) | Q4 (ground and wall) | Q8 (corner) |
|---|---|---|---|
| 3 m | 40.5 dB(A), fails | 43.5 dB(A), fails | 46.5 dB(A), fails |
| 5 m | 36.0 dB(A), passes | 39.0 dB(A), fails | 42.1 dB(A), fails |
| 8 m | 32.0 dB(A), passes | 35.0 dB(A), passes | 38.0 dB(A), fails |
| 10 m | 30.0 dB(A), passes | 33.0 dB(A), passes | 36.0 dB(A), passes |
Two things stand out. Doubling the distance cuts about 6 dB. Moving a unit out of a corner saves 3 dB for each reflecting surface removed. A solid brick garden wall that blocks the line of sight can be worth up to 10 dB, which is often what makes a tight site work.
Also think about your own bedrooms. The limit protects neighbours, but MCS noise guidance advises against siting the unit next to any sleeping area, including yours.
Should a Heat Pump Go at the Front or Back of the House?
A heat pump is usually best at the side or back of the house, because permitted development in England does not allow a unit above ground floor level on a wall facing a highway. In conservation areas and World Heritage Sites, the unit cannot go on any wall or roof facing a highway at all.
Other permitted development limits in England, in brief:
- The outdoor unit must be no bigger than 1.5 m³ on a house, or 0.6 m³ on a block of flats.
- Detached houses can have two units; other houses and flats can have one.
- Since 29 May 2025, a unit can sit within 1 metre of the boundary, provided it passes the noise calculation.
- Units cannot go on a pitched roof, and on a flat roof must be more than 1 metre from the roof edge.
- Listed buildings and scheduled monuments are not covered by permitted development.
Scotland, Wales and Northern Ireland have their own planning rules and still use the original MCS 020 noise method. We cover the full rules in our separate planning permission guide.
Is It Better to Mount a Heat Pump on the Wall or the Ground?
Ground mounting on a concrete base or plinth is better for most homes, because it is easier to service and less likely to pass vibration into the building. Wall brackets are useful where ground space is tight or flooding and snow are a risk.
For ground installs, Grant specifies raising the unit about 100 mm off its base on anti-vibration mounts, and leaving roughly 150 mm between the base and the house wall so the base does not bridge the damp-proof course. Grant’s anti-vibration mounts are not suitable for wall-mounted units.
Wall mounting has limits. Grant allows its Aerona 290 range on brackets rated to 250 kg, with the top of the unit no more than 2 m above ground. Heat pumps weigh anything from around 40 kg to over 100 kg, so the wall must be solid masonry in good condition. A wall-mounted unit on a thin wall next to a bedroom can transmit a low hum. Rubber isolation grommets on the brackets help.
Where Does the Condensate From a Heat Pump Go?
Condensate from a heat pump drains from the base of the outdoor unit and should go to a gravel soakaway, a gully or a drain, never across a path or patio. In cold weather, and after every defrost, the unit releases water that will freeze on hard surfaces.
Manufacturers set out specific methods:
- Grant asks for a trench at least 100 mm wide and deep around the base, filled with gravel or chippings, or a 40 mm waste pipe to a suitable drain.
- Vaillant specifies a downpipe to a gravel bed at a depth of at least 600 mm, or 900 mm in areas prone to frost.
- Daikin’s manual requires that the condensate cannot freeze once it has left the unit.
If the unit sits above a drive or path, the drainage needs planning before the base goes in.
Why Should You Avoid Corners, Enclosures and Air Recirculation?
Corners and enclosures make a heat pump noisier and less efficient, because reflecting surfaces raise the noise level and trapped cold air gets drawn back into the unit. Vaillant’s manual tells installers to avoid corners and spaces between walls or fences, and to prevent air from the outlet being drawn back into the intake.
A heat pump blows out air several degrees colder than the air it takes in. If that cold air cannot escape, the unit ends up breathing its own exhaust. Output drops and defrost cycles increase. Decorative enclosures and tight alleyways cause the same problem. If you want to screen the unit, use an open slatted design that respects the manufacturer’s clearances.
MCS noise guidance makes the same point from the acoustic side. Corners, enclosed areas and hollow spaces amplify noise.
How Far Can a Heat Pump Be From the House?
A monobloc heat pump has no fixed maximum distance from the house, but every metre of outdoor pipe loses heat and adds resistance, so shorter runs are better. A split system has a firm refrigerant pipe limit set by the manufacturer, typically between 20 m and 75 m depending on the model.
| Example system | Maximum pipe length | Maximum height difference |
|---|---|---|
| Mitsubishi Ecodan split PUHZ-SW50 | 40 m refrigerant | 30 m |
| Mitsubishi Ecodan split PUHZ-SW75 | 40 m refrigerant | 10 m |
| Mitsubishi Ecodan split PUHZ-SW120 | 75 m refrigerant | 30 m |
| Daikin Altherma 3 R split | 20 m refrigerant (3 m minimum) | 20 m |
| Monobloc (Grant Aerona³) | No stated maximum; water pipes sized and insulated | Not specified |
For monobloc units, Grant says all external pipework must be insulated with a vapour barrier. For a 28 mm pipe with insulation rated at 0.04 W/mK, that means at least 25 mm thickness. Long runs across a garden also need a trench and extra frost protection.
How Does a Monobloc or Split System Change Where Things Go?
A monobloc system keeps all the refrigerant in the outdoor unit and sends heated water into the house, so the water pipes between the two must be protected from frost. A split system sends refrigerant indoors to a hydrobox, which allows a longer run but must be connected by an engineer qualified to handle refrigerants under the F-gas rules.
| Factor | Monobloc | Split |
|---|---|---|
| What runs between units | Water (heating circuit) | Refrigerant |
| Frost risk outside | Yes; glycol or anti-freeze valves needed | No water outside |
| Pipe length | Keep as short as practical | Up to the manufacturer’s limit |
| Indoor space | Cylinder and controls; sometimes a volumiser | Hydrobox plus cylinder, or combined cylinder unit |
| Installer skills | Plumbing and electrical | Also F-gas refrigerant handling |
Grant recommends a 25% concentration of its thermal fluid, giving protection down to −12°C, where glycol is used. Anti-freeze valves are the alternative and must be fitted to the valve maker’s instructions.
Where Do the Indoor Parts of a Heat Pump System Go?
The indoor parts of a heat pump system, mainly the hot water cylinder, any buffer or volumiser and the controls, usually go in an airing cupboard, utility room, garage or loft space with enough headroom. A heat pump cylinder is taller or wider than most combi boiler homes expect, so plant space is often the tightest part of the design.
MCS design rules size the daily hot water demand at 45 litres multiplied by the number of bedrooms plus one, or the known occupants if higher. For example, a typical 3-bed semi would be designed for 180 litres a day. Kingspan’s Aerocyl heat pump cylinders give a sense of the space needed.
| Cylinder size (Kingspan Aerocyl) | Height | Diameter |
|---|---|---|
| 150 litres | 1,117 mm | 550 mm |
| 210 litres | 1,493 mm | 550 mm |
| 250 litres | 1,744 mm | 550 mm |
| 300 litres | 2,057 mm | 550 mm |
Add space for the expansion vessel, pipework, valves and service access. Some systems also need a volumiser or buffer; Grant, for example, requires a volumiser on all Aerona³ R32 installs unless a buffer or thermal store is already fitted. The controller and wiring centre can usually go on a nearby wall. If the airing cupboard is too small, a garage or utility room close to the outdoor unit keeps pipe runs short.
Where Can a Heat Pump Go in a Flat, Terrace or Small Garden?
In a terrace or small garden, a heat pump usually goes on a rear wall bracket or a compact ground plinth in the back yard, with a barrier between the unit and the nearest neighbouring window. Flats are harder.
For terraces, the noise calculation is often the deciding factor because neighbours’ windows are close. A solid brick yard wall, a spot away from the party wall corner and a quieter model can make the difference. The removal of the 1 metre boundary rule in England has made more small gardens workable.
For flats, permitted development allows one unit up to 0.6 m³ on a block of flats. Leaseholders also need the freeholder’s consent, and there must be somewhere suitable for the outdoor unit and the cylinder. Ground-floor flats with a garden are the most practical.
Which Heat Pump Locations Should You Avoid?
You should avoid placing a heat pump in corners, enclosures, next to bedroom windows, under low overhangs, over paths or anywhere the air cannot circulate freely. The table sums up the common mistakes.
| Location to avoid | Why |
|---|---|
| Corners or between walls and fences | Recirculated cold air and higher Q factor noise penalty |
| Beside a neighbour’s or your own bedroom window | Noise; likely to fail the 37 dB(A) check |
| Above paths, steps or patios | Condensate and defrost water freezes |
| Under deciduous trees | Leaves block the coil (Vaillant advises against) |
| Where snow drifts | Blocked airflow and ice build-up |
| Near openable windows, doors or drains (R290 units) | Refrigerant safety zones; Grant requires 390 mm from openings, 1,000 mm when wall-mounted, and 500 mm either side for gullies |
| Front walls above ground floor facing a road | Not permitted development in England |
Every home is different, and the best spot is often a compromise between noise, pipe length and appearance. A HomeKOG survey checks all of these on site before we recommend where the unit and cylinder should go.
