In many cases, you can install a reversible home air conditioning system in England without making a full planning application because qualifying air source heat pump installations can fall within permitted development rights.
The rules changed significantly on 29 May 2025. The old requirement to keep the outdoor unit at least one metre from the property boundary was removed, the permitted outdoor unit size for houses increased to 1.5 cubic metres, and reversible air to air systems capable of cooling and heating were explicitly brought within the permitted development rules. Important conditions still apply, particularly around noise, listed buildings, conservation areas, roof installations and the number of outdoor units.
At a Glance
Do most houses need full planning permission for residential air conditioning? Not necessarily. A qualifying reversible air to air heat pump installation may be permitted development if all relevant conditions are satisfied.
Has the old one metre boundary rule been removed? Yes. The Government removed the general requirement for the outdoor unit to be at least one metre from the property boundary in England from 29 May 2025.
How large can the outdoor unit be? For a house, the outdoor compressor unit including its housing must not exceed 1.5 cubic metres if relying on this permitted development right. For a block of flats, the limit remains 0.6 cubic metres.
How many outdoor units can a detached house have under these rights? Up to two qualifying air source heat pumps can potentially fall within permitted development on a detached house. For a house that is not detached, or a block of flats, only the first qualifying installation is permitted under this particular right.
Can the system provide cooling? Yes. The 2025 changes specifically allow air source heat pumps capable of cooling as well as heating. They must not, however, be used solely for cooling.
Can you install an outdoor unit on a pitched roof under permitted development? No.
Do listed buildings require extra consideration? Yes. The permitted development right does not apply within the curtilage of a listed building.
Reading time: 12 to 14 minutes
Last reviewed: August 2026
Why the Planning Rules Matter More Than Ever
Residential air conditioning is increasingly being installed as reversible heating and cooling rather than simply summer cooling.
Technically, most modern residential split systems are air to air heat pumps.
They move heat out of the property during summer and reverse their operation during winter to transfer heat indoors.
That distinction became particularly important when the Government changed permitted development rules in 2025.
The Warm Homes Plan confirms that the changes were intended partly to allow air source heat pumps capable of both heating and cooling to benefit from permitted development rights.
For homeowners considering fixed residential air conditioning, this is a significant change.
What Changed in May 2025?
Several important rules changed on 29 May 2025.
The One Metre Boundary Rule Was Removed
Previously, the air source heat pump had to be installed at least one metre from the property boundary.
That caused difficulties for many homes with narrow side passages or small gardens.
The Government removed this general restriction.
A qualifying installation can now potentially be positioned within one metre of the property boundary, provided all the other permitted development requirements are satisfied.
This does not mean outdoor units can simply be positioned anywhere.
Noise remains particularly important.
The installation must comply with the relevant MCS Planning Standard for noise.
The Size Limit Increased
For a house, the maximum permitted volume of the outdoor compressor unit including its housing increased from 0.6 cubic metres to:
1.5 cubic metres
For blocks of flats the limit remains:
0.6 cubic metres
Most normal residential split outdoor units are considerably smaller than 1.5 cubic metres, but the actual equipment should still be checked.
Detached Houses Can Potentially Have Two Heat Pumps
The amended rules allow up to two air source heat pumps on or within the curtilage of a detached dwellinghouse under the relevant permitted development right.
For a semi detached house, terraced house or block of flats, only the first installation can benefit under this particular provision.
This can be important when designing residential air conditioning.
For example, a detached property may suit two separate outdoor systems rather than forcing every room onto one large multi split.
Planning rules are therefore becoming more compatible with good air conditioning design.
Heating and Cooling Systems Are Now Included
This is particularly important for ClimateWorks customers.
The rules now expressly allow an air source heat pump capable of cooling as well as heating.
The condition is that the system must not be used solely for cooling.
Modern reversible residential air conditioning naturally fits this technology because the same equipment is capable of winter heating and summer cooling.
ClimateWorks Insight
The removal of the one metre boundary rule is probably the planning change that matters most to everyday residential installations.
Older online guidance still regularly tells homeowners that every condenser needs to be more than one metre from their boundary.
That is no longer the general rule in England.
But removing a fixed distance rule does not remove the responsibility to consider the neighbour.
Noise, airflow and sensible outdoor unit positioning still matter.
A technically permitted position can still be a poor installation position.
What Is Permitted Development?
Permitted development rights allow certain types of work to take place without submitting a conventional planning application.
They do not mean there are no rules.
The development has to satisfy every applicable limitation and condition.
For domestic air source heat pumps, Planning Portal states that the permitted development right can apply to installations on a house or block of flats, or within their curtilage, subject to the detailed requirements.
If one of those conditions is not satisfied, a planning application may be required.
The Noise Requirement Is Extremely Important
Removing the boundary distance restriction did not mean removing noise controls.
In fact, the revised planning framework places greater importance on acoustic assessment.
Planning Portal states that qualifying installations need to comply with the MCS 020a Air Source Heat Pump Sound Calculation standard.
From 28 May 2026, MCS 020a became the only permitted certification standard for this particular planning noise assessment.
This assesses the likely noise impact of the outdoor equipment at relevant neighbouring locations.
The Government has explained that this strengthened noise assessment allowed the older one metre boundary rule to be removed.
This is a much more logical approach.
An arbitrary distance does not tell you how noisy a system will actually be.
The equipment, sound power level, barriers, position and distance from neighbouring windows all matter.
Does This Mean ClimateWorks Must Be MCS Registered to Install Residential Air Conditioning?
The planning requirement should not be confused with the installer's F Gas obligations.
Planning Portal states that the installation must comply with the MCS Planning Standards.
That is a planning sound assessment requirement.
Separately, companies and engineers carrying out work on stationary air conditioning equipment containing fluorinated refrigerants must hold the appropriate F Gas certification and qualifications.
These are different regulatory considerations.
Homeowners should therefore avoid assuming that one certification automatically replaces another.
What About Semi Detached and Terraced Houses?
The revised rules distinguish between detached and non detached homes.
For a house that is not detached, only the first air source heat pump installation can benefit from this permitted development provision.
That matters when a homeowner is considering several outdoor units.
A typical three bedroom semi detached house may therefore be better suited to one multi split outdoor system if the homeowner wants several rooms air conditioned and wishes to remain within the relevant permitted development route.
However, system design should not be based on planning alone.
Pipework, capacity, redundancy and outdoor positioning still need consideration.
What About Detached Houses?
Detached properties have greater flexibility.
Up to two qualifying air source heat pump installations can potentially fall within permitted development, subject to the other conditions.
This creates useful design options.
One outdoor system might serve upstairs bedrooms.
Another might serve a ground floor living space or home office.
In some properties, that can produce a better installation than connecting every room to one large multi system.
What About Flats?
Permitted development rights can apply to a block consisting wholly of flats, but there are tighter restrictions.
The outdoor unit volume limit is 0.6 cubic metres.
Only the first qualifying air source heat pump installation benefits from this particular permitted development right.
Planning permission is also only part of the issue.
Flat owners commonly need to consider:
Freeholder permission.
Lease restrictions.
Managing agent approval.
Changes to communal or external areas.
The fact that something may be acceptable under planning law does not automatically give a leaseholder permission to alter the building.
Can an Outdoor Unit Go on a Roof?
This depends on the roof.
Planning Portal states that installations on a pitched roof are not permitted development under this right.
For installation on a flat roof, every part of the air source heat pump must be at least one metre from the external edge of that roof.
This is one area where the one metre rule still appears.
The general property boundary requirement was removed.
The flat roof edge condition was not.
That distinction is easy to miss.
What About Conservation Areas?
Conservation areas do not automatically make every installation impossible.
However, extra restrictions apply.
Within a Conservation Area or World Heritage Site, Planning Portal states that the air source heat pump must not be installed on a wall or roof fronting a highway or be closer to a highway bounding the property than any part of the building.
Visual impact becomes particularly important.
A discreet rear or side position may be very different from a condenser prominently mounted on a front elevation.
If there is uncertainty, speak to the local planning authority before installation.
What About Listed Buildings?
This is more restrictive.
Permitted development rights under this provision do not apply where the equipment would be within the curtilage of a listed building.
Listed building consent may also be relevant to alterations affecting the character or fabric of the building.
Homeowners with listed properties should therefore get proper planning advice before assuming a normal residential installation can proceed.
Can an Outdoor Unit Go on the Front of the House?
Potentially, but restrictions apply.
Outside Conservation Areas and World Heritage Sites, Planning Portal states that an air source heat pump cannot be installed above ground floor storey level on a wall that fronts a highway if relying on this permitted development right.
In practice, ClimateWorks generally prefers outdoor units to be positioned discreetly where suitable.
Rear elevations.
Side elevations.
Ground level positions.
Less visually dominant locations.
The best position must still provide adequate airflow and service access.
Do Planning Rules Replace Consideration for Your Neighbours?
No.
This is worth stating clearly.
Passing a planning sound assessment does not mean an installer should deliberately position the outdoor unit directly beneath a neighbour's bedroom window if a much better location exists.
Good residential design considers:
Noise.
Airflow.
Vibration.
Appearance.
Service access.
Future maintenance.
Neighbouring windows and outdoor spaces.
Planning compliance should be the minimum standard, not the end of the design process.
A Typical Hampshire Example
Imagine a semi detached home in Hampshire.
The homeowner wants air conditioning in three upstairs bedrooms.
There is only one attractive outdoor unit location down the side of the property, relatively close to the boundary.
Old guidance might immediately have suggested that this position failed because it was less than one metre from the boundary.
That rule changed in May 2025.
The position may now potentially fall within permitted development, subject to the other requirements including the MCS 020a noise assessment.
The design may then favour a multi split system serving the three bedrooms from one outdoor unit.
The planning changes give the installer more flexibility.
They do not remove the need for careful design.
A Typical Surrey Detached Home Example
Now consider a detached house requiring air conditioning upstairs and in a large ground floor kitchen.
The property has two excellent but separate outdoor unit locations.
Under the current permitted development rules, up to two qualifying air source heat pumps may potentially be allowed on a detached dwellinghouse without a full planning application, assuming every other requirement is met.
That may allow the air conditioning design to be separated into two systems rather than forcing the whole property onto a single outdoor unit.
This is a good example of planning rules supporting rather than restricting practical system design.
What If Permitted Development Rights Have Been Removed?
This is another important exception.
Planning Portal warns that permitted development rights can be removed by:
Planning conditions.
Article 4 Directions.
Other planning restrictions.
This can happen on particular developments or within certain areas.
New build estates may also have private covenants restricting external equipment.
A covenant is not the same as planning law, but it can still affect what a homeowner is allowed to install.
Common Planning Mistakes Homeowners Make
One of the biggest mistakes is relying on old online advice.
The one metre boundary restriction changed in 2025.
Another is assuming that permitted development means there are no conditions.
Noise still matters.
The outdoor unit size still matters.
The number of systems matters.
Roof positioning matters.
Property status matters.
Another common mistake is confusing planning permission with property permission.
A leaseholder may satisfy the planning rules and still require freeholder approval.
A homeowner on a private estate may have restrictive covenants.
Always look at the whole picture.
Dr Julian Carter's Expert Commentary
“The planning changes are positive for residential air conditioning because they recognise what modern systems actually are. A reversible air conditioner is an air to air heat pump providing heating as well as cooling. Removing the blanket one metre boundary restriction also gives installers more flexibility, but it puts greater responsibility on us to think properly about noise and neighbours. Permitted development should never be interpreted as permission to put the condenser wherever it is easiest to install.”
Dr Julian Carter
Technical & Compliance Director
ClimateWorks
How the ClimateWorks Process Works
Step 1. Get Your Online Guide Price
Use the ClimateWorks online quotation tool.
Tell us which rooms you are considering and receive an initial guide price.
Step 2. Request a Site Survey
If the guide price fits your expectations, request a site survey.
The outdoor unit position forms an important part of that assessment.
We consider the property type, equipment location, number of outdoor units, neighbouring properties, pipe routes and any obvious planning constraints.
Where formal planning advice or consent is required, this should be confirmed with the relevant local planning authority or planning professional.
Step 3. Receive Your Final Price
Following the survey, ClimateWorks provides a final quotation based on the agreed installation.
You can then accept or decline.
Why Homeowners Choose ClimateWorks
Planning rules are a good example of why residential air conditioning should not be treated as simply choosing a unit from a catalogue.
The equipment becomes part of the property.
The outdoor unit position affects the homeowner, neighbours and appearance of the building.
ClimateWorks works across Hampshire, Berkshire and Surrey designing systems around both technical performance and the practical constraints of the property.
The objective is not simply to find somewhere an outdoor unit is legally allowed to go.
It is to find somewhere it should go.
Frequently Asked Questions
Do I need planning permission for home air conditioning in England?
Not always. A reversible air to air heat pump installation may qualify as permitted development if all the relevant conditions are met.
Does an outdoor air conditioning unit still need to be one metre from my boundary?
No. The general one metre property boundary rule was removed in England in May 2025. Noise and the other permitted development requirements still apply.
What is the maximum outdoor unit size?
For a house, the outdoor compressor unit including housing must not exceed 1.5 cubic metres under this permitted development right. For a block of flats, the limit is 0.6 cubic metres.
Can a detached house have two outdoor units?
Up to two qualifying air source heat pumps can potentially be permitted development on a detached house, provided all other conditions are met.
Can a semi detached house have two outdoor units without planning permission?
Under this particular permitted development provision, only the first installation on a non detached dwellinghouse is covered. Further equipment may therefore require planning consideration.
Can air conditioning qualify if it provides cooling?
Yes. The rules now allow air source heat pumps capable of cooling and heating. The system must not be used solely for cooling.
Can I put my outdoor unit on a pitched roof?
Not under this permitted development right.
What is the rule for a flat roof?
Every part of the air source heat pump needs to be at least one metre from the external edge of the flat roof if relying on permitted development.
What is MCS 020a?
MCS 020a is the Air Source Heat Pump Sound Calculation standard used for permitted development noise assessment. Planning Portal states that from 28 May 2026 it is the only permitted certification scheme for this assessment.
Do the same rules apply across the whole UK?
No. The rules described in this guide relate to England. Planning law differs in Wales, Scotland and Northern Ireland. Planning Portal specifically warns that its England guidance should not simply be assumed to apply in Wales.
References
Planning Portal
Current Planning Portal guidance sets out the permitted development requirements for domestic air source heat pumps in England, including equipment size, number of units, roof restrictions, protected properties, noise standards and visual considerations.
UK Government Warm Homes Plan
Government guidance confirms that the May 2025 changes removed the one metre property boundary restriction, increased the outdoor unit size allowance for houses, increased the number of permitted heat pumps on detached homes and extended the right to systems providing both heating and cooling.
The Town and Country Planning General Permitted Development England Amendment Order 2025
The legislation came into force on 29 May 2025 and amended Class G of Part 14 governing domestic air source heat pump permitted development rights.
Author Bio
Dr Julian Carter is Technical & Compliance Director at ClimateWorks and specialises in residential air conditioning, air to air heat pumps and installation compliance. Drawing on practical experience from residential installations across Hampshire, Berkshire and Surrey, Dr Carter provides evidence based guidance to help homeowners understand the technical and regulatory considerations involved in installing permanent heating and cooling systems.
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