Planning constraints for ASHP

The domestic permitted-development tests for air-source heat pumps across the UK and when an application or heritage consent is needed.

Many domestic air-source heat pumps can be installed under permitted development, which is a national grant of planning permission. That does not mean every unit or position is permitted, and the rules are different in England, Wales, Scotland and Northern Ireland.

The position below is current to 22 July 2026. National guidance, local planning policy and property-specific restrictions determine the position for an individual installation.

England

Class G of the General Permitted Development Order covers installation, alteration or replacement of an air-source heat pump on a house or qualifying block of flats, within its curtilage or on another building in that curtilage. Every limit and condition has to be satisfied.

As at 22 July 2026, the principal tests include:

the installation must comply with MCS 020 a), which is the permitted certification scheme from 28 May 2026
an outdoor compressor unit including its housing can be no larger than 1.5 cubic metres at a house or 0.6 cubic metres at a block of flats
a detached house can use the right for its first two air-source heat pumps; a non-detached house or qualifying block of flats can use it for the first installation
a property with an existing wind turbine cannot use this right for an air-source heat pump
a unit on a pitched roof is not permitted development
every part of a unit on a flat roof must be at least one metre from the roof’s external edge
the right does not apply within the curtilage of a listed building or within a scheduled monument
additional highway-facing restrictions apply in conservation areas and World Heritage Sites
outside those designated areas, a unit cannot be above ground-floor-storey level on a wall that fronts a highway

The equipment must not be used solely for cooling. It must be removed when no longer needed for microgeneration and, as far as practicable, sited to minimise its effect on the building’s appearance and the area’s amenity.

The former general requirement to keep an English domestic unit at least one metre from a property boundary was removed in 2025. It should not be repeated as current English law. A boundary position can still fail the MCS noise test, the R290 manufacturer safety requirements, amenity conditions or another planning restriction.

The MCS 020 a) noise calculation

MCS 020 a) is a planning calculation, not a general product label. It predicts sound at defined assessment positions one metre outside neighbouring habitable-room doors or windows.

As at 22 July 2026, the permitted-development limit in the standard is 37 dB LAeq,5mins at those positions, ignoring the receiving facade effect. The calculation uses the unit’s sound power, distance, reflecting surfaces and qualifying barriers. It has a method for one or two heat pumps, and each potentially affected position is assessed.

Compliance with the noise calculation alone does not grant permitted-development rights. Unit number, volume, roof position, heritage restrictions and every other Class G condition still apply.

An installation that needs a planning application is not automatically unacceptable. The local authority may use a different acoustic assessment and consider the proposal on its particular facts.

Wales

Welsh permitted-development rules are more restrictive than England’s current Class G. Welsh Government guidance says one air-source heat pump used solely for heating is normally permitted where it complies with the MCS planning standard or equivalent and all other conditions are met.

As at 22 July 2026, the published conditions include:

no more than one unit on or within the property’s curtilage
an outdoor compressor unit, including housing, no larger than one cubic metre
no part within three metres of the property boundary
no existing standalone wind turbine within the dwelling’s curtilage
no installation on a pitched roof
at least one metre from the edge when on a flat roof
no wall or roof position fronting a highway

The unit must be positioned to minimise effects on appearance and amenity. Listed buildings, conservation areas and locally removed rights need checking with the council.

Scotland

Scottish Class 6H permits an air-source heat pump on a dwelling or within its curtilage, subject to its own limits and conditions.

As at 22 July 2026, it does not permit more than one unit on the same building or within its curtilage. A unit on a dwelling cannot project more than one metre from the external wall, roof plane, ridge or chimney. A curtilage installation cannot be forward of a principal elevation, or a road-facing side elevation, and the resulting structure cannot exceed three metres in height.

In a conservation area, a unit on a dwelling is restricted to ground-floor level on the rear elevation. The right does not apply in a World Heritage Site or within the curtilage of a listed building. The equipment must serve domestic heating or hot water, comply with MCS planning standards or equivalent and be removed when no longer needed.

Northern Ireland

Northern Ireland introduced domestic heat-pump permitted-development rights in 2023. Department for Infrastructure guidance says an air-source heat pump can proceed without an application subject to its limits, including being at least one metre from a neighbouring property boundary and complying with the prescribed noise standard.

The detailed Order and the property’s planning history should be checked before relying on the right. A general summary page is not a substitute for testing every condition.

Listed buildings and protected places

Planning permission and listed-building consent are separate controls. Work affecting the character of a listed building can require listed-building consent even where a planning right might otherwise exist. Pipe penetrations, external equipment, removed fabric and their visual effect all matter.

Scheduled monuments, World Heritage Sites, conservation areas and designated landscapes can introduce further restrictions or stronger design considerations. A discreet location may still be technically unsuitable for airflow, noise or R290 refrigerant safety.

Early discussion with the relevant conservation or planning officer is preferable to installing first and arguing later.

Rights can be removed

A planning condition, Article 4 direction or equivalent local control can remove or restrict permitted-development rights. Flats and leasehold properties can also require freeholder or landlord consent even when planning permission is not needed.

Permitted development belongs to the property and proposal, not to the installer’s accreditation. An MCS installer and an MCS 020 a) calculation do not restore rights that have been removed.

Where the position is important or future sale evidence is wanted, the owner can consider asking the local authority about a lawful-development certificate. That is different from a planning application and records the authority’s view that the proposal is lawful.

Building regulations and other approvals

Planning is only one approval stream. A heat-pump project can also involve:

building regulations for heating, hot water, structure and electrical work
DNO notification or prior connection approval
a highway or landlord consent
listed-building consent
environmental permissions for some ground or water-source systems

The project record identifies who obtains each approval. A statement that planning is not required is not evidence of the applicable planning position.

Planning record

The handover file should retain the dated planning assessment, site plan, unit dimensions, MCS 020 a) calculation, photographs and any correspondence, application, decision or lawful-development certificate.

If the unit, enclosure or position changes after that assessment, recheck it. A larger replacement model or a new fence can change the result.