Hillingdon: air conditioning planning permission

Since 2025-05-29, England's permitted-development rules let a house fit an air-to-air heat pump - which heats as well as cools - without a planning application in many cases, within set size, siting and noise limits. A cooling-only air conditioning unit does not get that route and needs a full planning application in Hillingdon whatever the property, because on its own it only cools.

Picking a system in Hillingdon therefore decides your planning path as much as your comfort. A unit that heats and cools opens up the permitted-development route on a house; one that only cools never does. Conservation-area coverage in Hillingdon is genuinely low (around 8% of EPC-certified homes), so for most addresses an external unit is a lower-friction proposition than in a heritage-dense borough - an honest advantage, not a workaround.

Flats are the sharpest exception here as everywhere in England: the permitted-development right for an outdoor unit sits with the house, not the flat, so a Hillingdon flat will usually need both freeholder or managing-agent consent and planning permission.

Planning is more straightforward in Hillingdon than in a lot of the country: only around 8.3% of properties sit inside a conservation area, so most houses can use the permitted-development route for an outdoor unit. Flats are still treated differently, and will usually need the London Borough of Hillingdon's planning permission for a front or side unit.

We hold some decided cooling cases for Hillingdon and not enough to say anything with. The sample-size floor is there precisely to stop a thin record turning into a confident-looking statistic.

What actually gets refused, and what councils attach when they approve, is a national picture rather than a local one at the volume of officer reasoning currently published. We set both out with their sample sizes: why cooling applications get refused and the conditions councils attach.

You can also compare what each council decides, where enough decisions exist to publish a figure.

Background noise in Hillingdon sits around 47 dB across the property types we profile during the day, which is the level any outdoor unit has to live inside. A machine that is inaudible on a busy street can be the dominant sound in a still garden, so the local baseline changes the answer.

That makes placement the thing to get right: distance from a neighbour's window, and distance from the boundary, do more for an application than the specification of the unit itself.

Nothing here is a dealbreaker. Hillingdon's council approves outdoor units for homes like these routinely. Conservation-area coverage locally runs at around 8.3%, which makes this worth planning for rather than assuming. Proximity to a listed building - around 1.3% of homes here sit within 30 metres of one does not mean your own home is listed, and public data can flag a conservation-area question without answering it. Treat this as indicative guidance, not legal advice, and confirm the final position with your Local Planning Authority before installing.