Planning guide (last updated autumn 2026)
Planning Permission for Air Conditioning in Hounslow - do you need it?
Most Hounslow homeowners can fit a wall-mounted split system without asking the council first, so without getting planning permission. The catch is that the exemption only covers certain units in certain positions, and not every building qualifies. Get one of those wrong and a straightforward install can turn into a letter asking you to take the outdoor unit down, and a big sunk cost.
These official rules around planning permission and AC do change a lot, they were last tweaked on the 28th of May 2026, and had another major adjustment on the 29th of May 2025. We gathered up to date and relevant information for homes in Hounslow as of autumn 2026, so you can rest assured you are making the right move.
- Based on the 2025 permitted development order
- Hounslow conservation areas and Article 4 included
Air con planning permission checker
Question 1 of 6
This page is a well-informed guide to the rules, but is not legal advice. You can confirm details with the Planning Portal or Hounslow Council.
Why most home AC installs don't need permission
In terms of planning law, a reversible air conditioner is treated as an air-to-air heat pump. In the 2025 amendment to the General Permitted Development Order (Part 14, Class G), air-to-air heat pumps received the same permitted development rights as the air-to-water heat pumps that replace gas boilers. Permitted development means the work is already granted planning permission by national law, it's essentially your right to install it, as long as a few conditions get met.
For a house, those conditions are:
| Condition | The rule for a house |
|---|---|
| Heating and cooling | The outdoor unit must not be used solely for cooling. It has to be a heat pump that can also heat the home. |
| Number of units | One outdoor unit on a semi-detached or terraced house. Two on a detached house. |
| Size | The outdoor unit (the compressor) must be no bigger than 1.5 cubic metres. |
| Roofs | It cannot go on a pitched roof. On a flat roof it has to sit at least 1 metre back from the edge. |
| Noise | The installation must meet the MCS 020(a) noise standard. In practice that means a calculation showing the unit will be no louder than 37 dB(A) at the nearest neighbour's habitable room window. |
| Appearance and removal | It must be sited to keep the effect on the look of the building and on neighbours as low as practicable, and removed when no longer needed. |
| Wind turbines | There must be no wind turbine on the building or in the garden. |
Before 2026, there was a rule keeping heat pumps at least 1m from the boundary, but that's now been taken out. So has the "or equivalent" noise route. Since the 28th of may 2025, the MCS 020(a) calculation is the only one that counts for permitted development.
For a home AC unit, the size limit is never really a factor. Typical AC units tend to measure at around 80cm wide by 55 tall by 30cm deep, around 0.13 cubic metres total. This is about a tenth of the allowance, so well within the limits. The key consideration is the unit count, the noise calculation and the cooling-only rule.
Sources: Planning Portal: air source heat pumps; The Town and Country Planning (General Permitted Development) (England) (Amendment) Order 2025.
The cooling-only trap
When you install a unit, it's not always obvious whether or not it actually has a heating function. That's why this often gets missed and ends up causing a lot of issues. If a unit is only cooling, then it does not get covered by Class G.
If your system can only cool, it needs planning permission (or a formal check with the council) anywhere it's installed. Lots of wall-mounted splits sold for homes are reversible, they heat as well as cool, but not all of them! You need to check that the model lists a heating mode before you buy it.
In legal terms, the wording is about how the unit is used as well as its capabilities. It can't just be used for the purpose of cooling. A reversible unit that you use for heating in the winter will sit comfortably within these rules.
When you do need planning permission in Hounslow
| Your situation | Planning permission needed? |
|---|---|
| Reversible split on a house, one outdoor unit at the back, noise calculation passes | No, it's permitted development |
| Cooling-only unit | Yes, or confirm with the council first |
| Listed building | Yes, plus listed building consent |
| Conservation area, unit on a wall or roof facing the road | Yes |
| Bedford Park or Gunnersbury conservation area | Check with the council; Article 4 directions apply |
| Second outdoor unit on a semi or terrace, or a third on a detached house | Yes |
| Flat, maisonette, or flat above a shop | Usually yes; see below |
| Outdoor unit on a pitched roof, or within 1m of a flat roof's edge | Yes |
| Noise calculation shows more than 37 dB(A) at a neighbour's window | Yes |
Air conditioning on a listed building
Permitted development rights for heat pumps do not apply to listed buildings at all. You will need planning permission, and listed building consent too. Drilling through walls for pipework and fixing a bracket to the outside both count as works to the listed fabric.
Listed building consent has no fee, but the application takes time and the council's conservation team will care a great deal about where the pipe run goes. If you are not sure whether your home is listed, search the National Heritage List for England before you book a survey. Carrying out unauthorised works to a listed building is a technically classed as a criminal offence, so this is the one case where "fit now, ask later" is a bad idea.
Conservation areas and Article 4 directions in Hounslow
Hounslow has 29 conservation areas. If you live in one, there are still ways to get air conditioning but it narrows where the outdoor unit can go. Under Class G, and as Hounslow Council's own guidance repeats, the unit must not be on a wall or roof that fronts a highway, or closer to a road than the nearest part of the house. In most cases that means the back wall or the rear garden.
Two areas go further. Bedford Park and Gunnersbury, towards Chiswick, have Article 4 directions that remove some permitted development rights for alterations to elevations and roofs. If your home is in either, speak to the council before assuming anything is permitted. You can check conservation area boundaries on the council's appraisal maps.
Check your address
- Open the council mapGo to Hounslow's conservation areas page and open the interactive map.
- Turn on the layerSelect Environment, then Conservation Areas, in the map layers.
- Find your streetA shaded area around your address means it's in a conservation area.
See also the Article 4(2) directions for Bedford Park and Gunnersbury and the council's guidance on permitted development, conservation areas and listed buildings.
Flats and maisonettes
Flats are where the rules get awkward. Class G does cover "blocks of flats", but only buildings made up entirely of flats - and there are plenty of flats in Hounslow above shops, that don't fall under this classification.
It allows one outdoor unit for the whole block, no bigger than 0.6 cubic meters. If a neighbor in your block has already fitted one under permitted development, yours will need permission. A flat in a mixed-use building, such as one above a shop, falls outside Class G entirely.
Planning is only half of the job. Most leases will need the freeholder's written consent for anything fixed to the outside wall, and that is a separate permission from the council's.
More outdoor units than the limit
One outdoor unit on a terrace or semi sounds restrictive if you want AC in three bedrooms. A multi-split gets round this. One outdoor unit can run several indoor units, so a two-to-five-room multi-room setup can often stay within the one-unit limit where three separate single splits would not.
Noise near neighbours
The 37 dB(A) limit is measured at your neighbour's nearest habitable room window, allowing for distance, walls and fences in between. On the tight terraced streets of TW3 and TW4, a unit mounted on a back wall a couple of metres from next door's bedroom window can fail the calculation where the same unit at the end of a garden would pass. Your installer should run the MCS 020(a) calculation before fitting and give you a copy. If the numbers don't work, the usual fixes are moving the unit or adding an acoustic enclosure; failing that, you apply for permission.
How to be certain before you install
If your install clearly meets every condition above, you don't need to tell the council anything. Where there is doubt, you have three options.
- Apply for a Lawful Development Certificate. This is a formal confirmation from the council that your proposal is permitted development. The fee is half the equivalent planning application fee, and Hounslow's 2026 to 2027 fee schedule sets the householder fee at £548, so expect about £274. It is also a handy document to have when you come to sell.
- Ask for pre-application advice. Hounslow encourages this for anything in a conservation area or on a listed building.
- Apply for householder planning permission (£548) if you already know the install falls outside permitted development.
For an ordinary house, installing without permission when you needed it is not a crime in itself (listed buildings are the exception), but the council can take enforcement action and require the unit to be removed. A retrospective application is possible, though you are then arguing for a unit that is already on the wall.
Permissions that aren't planning permission
F-Gas certification
The engineer handling refrigerant must hold an F-Gas certificate. This is a legal requirement for anyone connecting or charging an AC system.
Electrical work
New electrical circuits fall under Part P of the Building Regulations, so the electrical work needs to be done by a registered electrician who can self-certify it, or signed off by building control.
Freeholder consent
Leaseholders need freeholder consent, as above.
Noise nuisance
Even a permitted unit can still be investigated as a statutory noise nuisance if it disturbs neighbours, so siting matters beyond the planning test.
What to do next
A reversible split on the back of a house, outside a conservation area, usually needs nothing from the council. Anything else in the table above is worth checking first. When you book a survey, ask the installer to confirm in writing that the system and position you want fall within permitted development, and to show you the MCS 020(a) noise calculation. If the first-choice spot doesn't work, a different wall or a multi-split often will. You can see the postcodes we cover on our areas page.
Request a SurveyAir conditioning planning permission: common questions
Do I need planning permission for air conditioning in Hounslow?
Usually not, for a house. Since 29 May 2025, air conditioning that heats as well as cools counts as an air source heat pump and is permitted development in England, subject to limits on size, number of units, position and noise. Listed buildings, cooling-only units, flats and units on walls facing a road in a conservation area are the main exceptions.
Does portable air conditioning need planning permission?
No. A portable unit sits inside the room and vents through a window kit, so there is no external development.
Does my neighbour need to agree to my air conditioning?
No, not under permitted development. The installation must still pass the MCS 020(a) noise calculation, which limits sound to 37 dB(A) at the neighbour's nearest habitable room window.
Last checked against the Planning Portal and Hounslow Council guidance: September 2026. This page is a guide, not legal advice.
Arrange a survey with a planning check
Tell us your postcode and the rooms to cool, and we'll put you in touch with a local F-Gas certified installer who covers your area. The survey confirms the unit position and whether anything needs an application before you commit.