Air Conditioning Outdoor Units

Every split air conditioning system has an outdoor unit. It holds the compressor and a large fan, and it is where the heat from your rooms is released in summer and collected in winter. Where it goes affects how well the system works, how much your neighbours hear it and whether you need planning permission. This guide covers placement, the rules, noise and covers.

What Does the Outdoor Unit Do?

In cooling mode, the outdoor unit releases the heat taken out of your rooms, which is why it blows warm air. In heating mode, it does the opposite and collects heat from the outside air. Inside are the compressor, a coil and a fan. Our guide on how air conditioning works explains the process.

Where Can the Outdoor Unit Go?

• On a wall bracket, often on a rear or side wall, which keeps it off the ground and away from leaves and standing water.

• On the ground, on a solid base or a stand that lifts it clear of the ground.

• On a flat roof, at least 1 metre from the edge for permitted development.

• On a balcony or terrace, with enough space around it for airflow.

Many wall units allow up to 20 metres of pipework between the indoor and outdoor units, so the outdoor unit can often go somewhere out of sight. If there is nowhere for one at all, see air conditioning without an outdoor unit.

What Makes a Good Position?

• Free airflow. The unit needs open space in front and the clearances behind and to the sides that the manufacturer specifies. Boxed in, it draws in its own exhaust air and has to work harder.

• A short pipe route to the indoor unit.

• A solid fixing, on a sound wall or a firm base, with anti-vibration mounts to reduce noise passing into the building.

• Distance from bedroom windows, yours and your neighbours', where possible.

• Safe drainage. In heating mode, the unit produces water when it defrosts, so it should not drip onto a path or doorstep where the water could freeze.

• Access for servicing.

Do You Need Planning Permission?

For most houses in England, no. Since 29 May 2025, air conditioning that heats as well as cools has been covered by permitted development rights, as long as the outdoor unit:

• is no larger than 1.5 cubic metres, or 0.6 cubic metres on a block of flats

• meets the MCS 020(a) noise standard

• is not on a pitched roof, and is at least 1 metre from the edge of a flat roof

• is the only one on the property, or one of no more than two on a detached house

• in a conservation area, is not on a wall or roof facing a road

• outside a conservation area, is not on a wall facing a road above ground-floor level

The old rule that the unit had to be at least 1 metre from the boundary was removed in May 2025. Listed buildings, flats and systems used only for cooling follow different rules. See our planning permission guide and our guide to air conditioning for flats.

How Loud Is an Outdoor Unit?

The outdoor unit is louder than the indoor unit because it holds the compressor and the main fan. Under permitted development, the installation must meet the MCS 020(a) noise standard, which sets a limit of 42 dB(A) at the nearest window of a neighbouring home. Distance, screening and position all make a difference, so we plan the position with you and your neighbours in mind. Many systems also have a night or quiet mode that reduces outdoor unit noise. See the quietest air conditioners.

Should You Cover the Outdoor Unit?

Generally, no. Outdoor units are built to sit outside all year, in rain, wind and frost, and most manufacturers advise against covering them.

• Never cover a unit you use for heating. In winter it needs a free flow of outside air to collect heat, and a cover stops it working properly.

• Covers trap moisture, which can lead to corrosion and mould, and they can give mice and insects a sheltered place to nest.

• A forgotten cover can cause the system to overheat or be damaged when it is switched on.

In an exposed spot, a top canopy or a screen that leaves plenty of space for air to flow can help keep falling leaves and heavy snow off without blocking the airflow. Check the manufacturer's instructions before fitting anything, as some covers can affect the warranty.

Looking After the Outdoor Unit

• Keep leaves, plants and garden clutter well clear of it.

• Brush off leaves and debris gently, and never use a pressure washer.

• After heavy snow, clear the snow from around the unit so air can flow. The unit clears ice from its own coil with a defrost cycle.

• Water, and sometimes a little steam, from the unit in winter is normal. It comes from the defrost cycle.

• Have the system serviced every year, or twice a year if you use it for heating. See our air conditioning servicing page.

Frequently Asked Questions

Can the outdoor unit go inside, in a garage or loft?

Not an ordinary outdoor unit. It needs a large, free flow of outside air, and in an enclosed space it would heat the space up and stop working properly. A water-cooled unit can go indoors, at a higher cost to buy and run. See air conditioning without an outdoor unit.

Can it go on the front of the house?

It can, but in a conservation area it would need planning permission. Outside a conservation area, a unit on a wall facing a road must be at ground-floor level to count as permitted development.

How far can the outdoor unit be from the indoor unit?

It depends on the model. Many wall units allow around 15 to 20 metres of pipework, and larger units allow more. Every system has to be designed within the manufacturer's limits.

Can I build a box around it?

Only if it leaves plenty of open space for airflow on every side the manufacturer specifies. A tight box makes the unit draw in its own exhaust air, which cuts efficiency and can damage it.

Call 01772 288651 or use the form below to book a free survey. We will measure the room, recommend the right system and give you a clear written quote.

Last updated: November 2026.