Where should an outdoor air source heat pump unit be installed?

What to know first

These points cover the checks that should decide an outdoor unit’s position.

An outdoor heat pump unit should go where it can exchange air freely, drain safely, meet noise and planning requirements, and remain accessible. For many homes, that makes stable ground near an external wall the practical starting point. Wall brackets and roof sites can work, but need extra checks.

No universal distance from a wall, window or boundary suits every model and home. The installation manual, site survey and local rules all matter.

Where is the best place to start?

Begin with a level, open-air position on firm ground and a sensible pipe route. Test it against the exact model’s airflow and service clearances, drainage, the MCS sound calculation and planning restrictions. Energy Saving Trust says a unit can be wall mounted or ground mounted and needs surrounding space for airflow.

This is a practical starting point, not an official preference. Ground may be wrong where it floods, blocks a route, sits in a tight courtyard or creates a poor noise path.

Ground, wall or roof: how the locations compare

This table is a starting point. The final choice depends on the model, survey, sound calculation and permissions.

MCS counts nearby hard surfaces as sound reflectors. Ground plus one wall is two surfaces; corners add more. Its method says a small lightwell with more than three reflective surfaces will not meet MCS 020 a.

The roof assessment is an editorial inference, not a universal MCS rule. Equipment at height creates site-specific structural, weatherproofing and maintenance questions, so roof mounting is normally specialist work.

Expert insight

“Do not solve only one problem. The shortest pipe route can still be wrong if it creates poor airflow, unsafe drainage or a worse noise path.”

Giles Crosse

Energy Editor

Experienced editor, journalist and communications consultant specialising in consumer energy and low carbon technologies.

• Editor and campaign author for Shell, EDF Energy and Good Energy.
• Consultant to the United Nations and contributor to the World Economic Forum.
• Journalist for Reuters, the BBC, The Economist and The Guardian.

More about Giles Crosse

Give the unit clear air

The unit takes heat from passing air and releases colder air. Drawing that discharged air back in is called recirculation and can hinder operation. Avoid sealed cupboards, tight alleys, dense planting and screens that block the required air path.

Energy Saving Trust’s advice is direct:

Do not copy a generic clearance from another installation. Ask the installer to mark the exact intake, discharge and service zones. Any enclosure should be compatible with the manufacturer’s instructions and acoustic assessment.

Treat noise as a design issue, not a boundary measurement

For domestic permitted development, MCS 020 a Issue 1.1, dated 14 April 2025, sets the sound calculation. It tests a calculated five-minute average of no more than 37 dB(A), adjusted for human hearing, at each assessment position while ignoring façade reflection.

An assessment position is one metre outside the centre of a neighbouring door or window serving a living or sleeping room. Several positions and floors may need checking; the closest is not always the worst. Flats in the same block can count as neighbouring properties.

The installer must use the unit’s sound power level, not a brochure’s sound pressure figure, and cannot use low-noise mode for this calculation. Nearby ground and walls can raise the result through reflection.

Boundary distance alone does not prove compliance. Open or damaged fencing and vegetation do not count as acoustic barriers under MCS; qualifying solid barriers have detailed construction and sight-line tests.

Your own bedroom window is not the formal MCS position, but still matters for comfort. Wall brackets may also transmit vibration. A government-commissioned review found complaints were infrequent overall, while location, proximity, vibration and poor installation featured in cases examined.

Good to know

Ask for the completed MCS sound calculation. The contractor must give the customer a copy.

Plan drainage for cold, wet weather

Heat pumps can enter a defrost cycle in cold conditions and release water at the outdoor unit. Details vary by model. One current Grant unit, for example, has a heated base tray and several condensate drain holes.

Water should not pool beneath the unit or cross a doorway, path or steps where it could freeze. Keep the level base and drainage route accessible.

Leaves can obstruct the coil area or drainage. The government-commissioned review records manufacturer advice to clear leaves before winter. In snowy or exposed places, any protection must preserve airflow.

Keep pipework practical and leave room to service the unit

A direct route can reduce exposed pipework, but it is only one factor. A monobloc carries water from the outdoor unit to the home; a split system divides components between outdoor and indoor units. This changes the pipe route and model-specific frost-protection requirements.

Ask the installer to show pipes, cables, isolators and drainage on the survey drawing. Doors, gates and bins should not block the unit, and a technician should be able to reach its service panels.

Appearance matters, but dense planting or a close box can undermine airflow and access. Landscaping outside the required clearances may be a better compromise.

Check planning and permissions before fixing the location

Most domestic heat-pump installations are treated as permitted development, but exceptions apply. Energy Saving Trust advises checking the local planning department, especially for listed buildings and conservation areas.

Planning is devolved, so rules differ across the UK. MCS points to the English planning order and says other countries may differ. Scotland has specific Class 6H limits; Northern Ireland’s official advice says to ask the council whether proposed work meets permitted-development conditions.

MCS states:

Separate freeholder, managing-agent, landowner or listed-building consent may apply. Scotland’s consumer page, for example, tells residents to check with the council and obtain landowner or listed-building consent where needed.

Good to know

Confirm permissions before ordering equipment. Passing the sound calculation is only one part of the planning test.

Use a seven-step siting check

1. List realistic sites. Compare ground, wall and any specialist roof option.

2. Check the exact model. Confirm dimensions, sound power, clearances, service space and drainage.

3. Trace the air path. Rule out walls, screens or planting that block air or cause recirculation.

4. Run the sound calculation. The MCS contractor should assess every potentially affected neighbouring living or sleeping-room opening.

5. Design the base and drainage. Decide how the unit stays level and where defrost water goes.

6. Map routes and access. Show pipes, cables and the space needed for servicing or replacement.

7. Confirm permissions. Check planning and any listed-building, freeholder or landowner requirements.

If no site passes, consider another outdoor-unit model, a revised design, a planning application or another heating option. MCS says moving the unit may bring a failed sound calculation within the permitted-development limit.

What could make a difficult location cost more?

There is no official fixed “siting premium”. As a practical inference, a quote may rise for stronger bases or brackets, protected pipework, drainage, acoustic treatment, scaffolding, lifting equipment or structural checks. Ask for site-specific items to be separated from the headline installation price.

An MCS-certified installer should lead the design and sound calculation. Ask the planning authority where status is uncertain. Roof proposals may need structural input; complex full-planning cases may need an acoustician.

Key takeaways

• Ground near an external wall is often the practical starting point, not a rule.

• Airflow, drainage, noise and service access outweigh appearance alone.

• Do not rely on a generic wall, window or boundary distance.

• Current MCS calculations use a 37 dB(A) limit at defined neighbouring positions.

• Wall and roof sites need extra vibration, structure and access checks.

• Confirm planning and other consents before installation.

Frequently asked questions