Most houses in England can fit an air source heat pump without applying for planning permission. The work counts as permitted development if the outdoor unit is no bigger than 1.5 cubic metres, sits in an allowed position and meets the MCS 020a noise standard. Listed buildings, flats and some conservation area positions are different. This guide covers England only. The rules in Wales, Scotland and Northern Ireland are not the same.

What is permitted development for a heat pump?

Permitted development lets you do certain work without a planning application. For heat pumps, the rules sit in Class G of Part 14 of the General Permitted Development Order. They cover installing, altering or replacing an air source heat pump on a house or a block of flats, or within its grounds, including on an outbuilding.

A planning condition or an Article 4 Direction can remove these rights. Your local planning authority can tell you if that applies.

How big can the outdoor unit be?

On a house, the outdoor unit can be up to 1.5 cubic metres, including any housing around it. On a block of flats, the limit is 0.6 cubic metres.

We check the volume of the model we propose against the limit before we quote.

How many units can I have?

A detached house can have two air source heat pumps under permitted development. A semi-detached or terraced house can have one. A block of flats can have one. Any unit beyond that needs a planning application.

Where can the unit go?

Walls facing a road. Outside conservation areas, the unit cannot go on any part of a wall above ground floor level if that wall faces a highway. On the ground floor, it can.
Roofs. A pitched roof is not allowed. On a flat roof, every part of the unit must be at least one metre from the outside edge.
Looks and neighbours. The unit must be sited, as far as practicable, to keep its effect on the look of the building and on neighbours’ amenity to a minimum.
Wind turbines. If you already have a wind turbine on the building or in the grounds, a heat pump does not qualify.

There used to be a rule keeping the unit at least a metre from your boundary. It was removed on 29 May 2025, so a unit can now go closer to the fence, as long as it meets the noise standard.

What is MCS 020a?

MCS 020a is the noise standard for heat pumps fitted under permitted development. Its full title is “Air Source Heat Pump Sound Calculation (For Permitted Development Installations)”. It sets out a calculation of how much sound the unit will make at the neighbouring homes around it. If the calculation passes, the position qualifies. If it fails, you need a quieter unit, a different spot or a planning application.

The Order names MCS 020a as the standard a heat pump must meet. MCS itself says the standard applies whether or not the installation is MCS certified. It is a planning test on the unit and its position, not a badge for the installer. According to the Planning Portal, from 28 May 2026 MCS 020a is the only certification scheme accepted for this.

We run the MCS 020a calculation for the position we propose and show you the result.

What about listed buildings and conservation areas?

Permitted development does not apply to a heat pump on a listed building or within its grounds, or on a scheduled monument. You need to apply to the council.

In a conservation area or a World Heritage Site, the unit cannot go on a wall or roof that faces a highway. It also cannot be nearer to a road that borders the property than any part of the house.

Does a cooling-only unit count?

Class G has a condition that the heat pump is not used solely for cooling. A unit that only ever cools falls outside it.

Air-to-air heat pumps, the kind that heat and cool a room, are less clear. The Order does not define an air source heat pump, and we have not found a primary source that says air-to-air units sit under the same rules. Some installers say they do. We would rather not guess, so we check this for your home at the survey. You can read more about these units on our air conditioning page.

What if I fall outside permitted development?

You can still have a heat pump. You apply for planning permission to your local planning authority, and they decide. A third unit, a unit on a listed building, or a spot that fails the noise calculation all go this way.

If anything about your house is borderline, ask the council’s planning team before you commit. We explain the rules as they stand, but we are not your legal adviser, and the council has the final word.

A quick summary

Rule	House	Block of flats
Outdoor unit volume	Up to 1.5 cubic metres	Up to 0.6 cubic metres
Number of units	Two if detached, one otherwise	One
Noise	Must meet MCS 020a	Same
Wall facing a road	Ground floor only, and not at all in a conservation area	Same
Listed building	Apply to the council	Same
Reviewed	18 September 2026	18 September 2026

How we handle planning

Every air source heat pump we design starts with a survey. We look at where the unit can go, run the noise calculation and check the unit against the limits. If your home needs a planning application, we tell you before you spend anything.

If you are weighing up a heat pump and want to know where you stand, get in touch. We are happy to take a look.

Figures reviewed 18 September 2026.

heat pumpsplanning

Heat pump planning permission: the 1.5 cubic metre rule and MCS 020a explained