It’s one of the first questions we get asked, usually right after “how much will this cost?” Someone’s decided they’ve had enough of sweltering through another London summer, they’ve picked out a system, and then it suddenly occurs to them: do I actually need permission to fit this on the side of my house?

The good news is that most homeowners never need to go anywhere near their local council. But the rules changed in 2025, and there are a few situations, particularly common across London, where planning permission for air conditioning genuinely is required. Here’s what actually matters.

Indoor units are never the issue

Whatever system you choose, the wall-mounted unit inside your living room or bedroom doesn’t trigger planning permission of any kind. It’s the bit outside your home, the condenser, that the rules are concerned with. So if you’re only thinking about the visible box on your wall indoors, you can stop worrying and focus on where the outdoor unit is going to sit.

The rule that catches people out: cooling-only vs heating-capable

This is the part most people don’t realise, and it’s the single biggest change to the rules in recent years. Permitted development rights for these external units (under what’s known as Class G of the General Permitted Development Order) only apply if the unit can provide heating, not just cooling. A pure air conditioning unit that only cools will not qualify, and would need a full planning application. A reversible system, often sold as an air-to-air heat pump but doing exactly the same job as air con plus heating, generally will.

In practice, this means the type of system you choose has a direct bearing on whether you need to apply to your council at all. It’s one of the reasons it’s worth having a proper conversation with your installer before you commit to a unit, rather than after it’s already on order.

What “permitted development” actually requires

Assuming your system qualifies, the outdoor unit still has to meet a set of conditions to avoid a planning application:

• It needs to meet recognised noise standards (MCS 020, which has become the standard certification route for these installations).
• On a house, the unit can be up to 1.5 cubic metres, with up to two units allowed on a detached house or bungalow, and one on a semi-detached or terraced property. Blocks of flats have a smaller volume limit.
• It can’t go on a pitched roof, and if it’s mounted on a flat roof, it needs to sit at least a metre back from the edge.
• It should be positioned to keep its impact on how the building looks, and on neighbours, to a minimum.

Meet those and you don’t need to apply for anything. Miss one and the exemption falls away.

Flats, leasehold properties, and shared buildings

If you live in a flat, don’t assume the same freedoms apply. Permitted development rights for these units still exist for blocks of flats, but the volume allowance is lower, and there’s an added layer that has nothing to do with planning at all: your lease. Freeholders and management companies can, and often do, require their own consent before anything goes on an external wall or balcony, regardless of what the council says. It’s worth checking your lease before your heart is set on a particular installer or unit.

Listed buildings and conservation areas

This is where a lot of our enquiries from north and central London come from. Areas like Hampstead, Highgate, Kensington and parts of Marylebone include a fair number of listed buildings and conservation areas, and the rules are stricter there by design. If your property is listed, you’ll typically need listed building consent on top of any planning permission, and councils tend to take a firm line on anything visible from the street. An Article 4 direction, which some conservation areas have in place, can remove permitted development rights entirely, meaning even a fully compliant system would need an application. If you’re not sure whether your street is affected, your local planning department can tell you in a phone call.

Commercial properties

For businesses, it’s safest to assume planning permission will be needed. Commercial systems are usually larger, often involve more than one external unit, and don’t get the same permitted development allowances as a family home. We’ve worked on plenty of commercial installations across London, from offices to restaurant kitchens, and the pattern is consistent: get the planning conversation started early, because it tends to take longer than the installation itself.

Our advice

Planning rules aren’t there to make your life difficult, they’re there so a condenser unit doesn’t end up too close to a neighbour’s window or bolted onto the front of a listed Georgian townhouse. In the vast majority of straightforward residential installations across London, Essex, Hertfordshire and Kent, a well-placed, appropriately sized unit will fall under permitted development and you won’t need to apply for anything.

Where it gets more complicated, listed buildings, conservation areas, flats, or commercial premises, it genuinely pays to have that conversation before the unit arrives rather than after. A good installer should be able to tell you within a few minutes of looking at your property and postcode whether you’re likely to need permission, and can help position the unit to keep you within the rules where possible.

If you’re weighing up a new system and want a straight answer on where you stand, get in touch with our team or give us a call on 020 8989 8989. With 25 years installing air conditioning across London, it’s a question we’re asked most weeks, and one we’re always happy to talk through before you commit to anything.

Here’s something most people don’t know: a blocked filter is behind a surprising number of air con problems. The unit running but not cooling properly. Energy bills going up without an obvious reason. That musty smell when it first kicks on after a few months off. None of that usually needs an engineer. It needs a filter clean, and knowing how to clean air con filters properly takes about fifteen minutes.

What the Filter Actually Does

Air gets pulled through the filter before the unit circulates it. Everything floating around the room, dust, pet hair, pollen, general household debris, gets caught in the mesh. That’s the point of it. The problem is that over time the build-up restricts airflow, and a unit pushing air through a blocked filter has to work harder to do the same job. Harder work means more energy, more wear, and eventually something giving up earlier than it should.

The air quality side of it is worth mentioning too. A filter that’s full isn’t cleaning the air properly anymore. For anyone with allergies, that matters. For everyone else it just means the room smells slightly off and you can’t work out why. This is exactly why understanding how to clean air con filters is worth a few minutes of your time.

How Often

Every two to four weeks during heavy use is the standard advice. If the unit runs every day through summer, check it monthly. Rooms with pets or higher dust levels need it more frequently.

Honestly though, you don’t need a schedule. Just pull the filter out every so often and look at it. Grey and coated means clean it. Still looks reasonable means put it back. Knowing how to clean air con filters takes five minutes to learn. Remembering to actually do it is the harder part.

How to Clean Air Con Filters: The Actual Process

Off first: Turn the unit off before doing anything: Not just the remote, the unit itself.

Front panel open: On most wall-mounted split units the front panel lifts upward or unclips at the bottom. If it’s not obvious, the manual will show you. The filters sit just behind it, usually two thin mesh panels that slide or clip out without any tools needed.

Take them out carefully: They’re light and they shed dust easily. If you’re inside, have a bag ready or carry them straight outside before the dust gets a chance to go everywhere.

Vacuum first: Soft brush attachment, gentle strokes across the surface. Takes the bulk off without spreading it around. Don’t press hard into the mesh.

Rinse under a tap: Lukewarm water, gentle flow, no scrubbing. Most filters handle this without any issues at all. Hot water can warp the mesh. Strong cleaning products leave residue that ends up getting blown into the room. Warm water is enough.

Dry them properly: This is where people cause problems. A filter going back into the unit while still damp creates conditions for mould and can damage internal parts. Lay them flat somewhere with a bit of airflow. Give it at least an hour. Don’t try to speed it up with a hairdryer on a high heat setting.

Back in, switch on: Refit the filters, close the panel, turn the unit on. If they were badly blocked the difference in how it runs is usually noticeable immediately.

Common Mistakes

What people try the most is cleaning the filters in the dishwasher, the reason this isn’t recommended is because heat and pressure warp the mesh. The residue doesn’t fully rinse away and ends up being circulated around the room. Warm water will be the safest option and most effective in cleaning those difficult areas.

Another common mistake that people do is fitting the filters that are still wet after cleaning. It’s crucial mentioning again because it’s the most common thing that causes problems after a filter clean.

Ignoring damage. Torn mesh or a cracked frame means the filter needs replacing, not cleaning. A damaged filter lets unfiltered air through and the whole exercise becomes pointless. If you’re learning how to clean air con filters and they keep looking damaged on inspection, replacement is the answer.

When a Clean Won’t Fix It

Knowing how to clean air con filters is useful. It won’t fix everything. If the unit is still struggling after the filters are clean, something else needs looking at. Dirty coils, low refrigerant, a component that’s on its way out. These are engineer jobs, not DIY ones.

If the system hasn’t had a professional service recently, it’s worth booking one before the next heavy-use period. How to clean air con filters is useful knowledge, but a service covers what a filter clean can’t reach. Issues that seem minor in May have a way of becoming urgent in July. Air Conditioning Direct has been installing and maintaining systems across London, Essex, Hertfordshire, and Kent for over 25 years. We cover residential and commercial systems, all our engineers are fully qualified, and we include up to a 7-year guarantee on selected equipment.

If you are unsure if your air conditioning system is working correctly then get in touch with our team today and we can help you find the root of the problem.