What Was the 1m Rule for Heat Pumps — and What Replaced It?

Before 29 May 2025, England's permitted development rules said an air source heat pump had to be at least 1 metre from the property boundary, the outdoor unit could be no bigger than 0.6 m³, and each home could have only one. If you couldn't meet all three, you needed planning permission. The 1m rule hit terraced houses hardest: many back yards and side passages are narrower than 2 metres, so there was simply nowhere compliant to put the unit.

Removing the 1m rule didn't remove every condition. You still need planning permission if:

• The unit would go on a pitched roof.
• It would go on a flat roof within 1 metre of the roof's edge.
• The property is a listed building or within its curtilage.
• You're in a conservation area or World Heritage Site and the unit would be on a wall or roof facing a road, or nearer the road than the house.
• It's a flat in a building that also contains commercial premises.
• The installation fails the MCS 020(a) noise assessment.

Wales, Scotland and Northern Ireland have their own permitted development rules and still use the original MCS 020 standard, so check with your local planning authority there.

MCS 020(a) is the noise calculation your installer carries out. It works out the sound level from the unit at the nearest neighbour's door or window, allowing for distance, walls, fences and reflective surfaces. If the result is 37 dB(A) or lower, the installation meets the permitted development condition. It also sets the method for homes with two heat pumps. An MCS-certified installer should give you this calculation before fitting — ask for it.

Greater Manchester has thousands of Victorian and Edwardian terraces with small back yards, and these were the homes the 1m rule most often ruled out. They can now qualify if the noise assessment passes, which usually comes down to picking the right unit and position. Parts of Didsbury and Chorlton are conservation areas, so there the unit normally needs to go at the back or side rather than on a wall facing the street.

See our air source heat pump installation in Manchester

Every Greentech survey includes the MCS 020(a) noise calculation and a positioning plan for the outdoor unit. If your property needs planning permission — for example a listed building or a street-facing wall in a conservation area — we tell you before you commit and can help with the application. The Boiler Upgrade Scheme grant still applies either way.