An air source heat pump installation by Architecture for London.
While gas central heating systems are enclosed within the building, an air source heat pump (ASHP) – the most common type of heat pump in the UK – requires an outdoor unit.
A common question homeowners ask is whether ASHPs require planning permission.
In many cases, air-to-water (A2W) ASHPs – which connect to radiators and underfloor heating – can be installed without planning permission.
However, air-to-air (A2A) systems – which connect to indoor fan units – usually do require planning permission as they are classified as air conditioning.
If you're considering an air-to-water ASHP, read our 3-step guide to understand what might be feasible for your home.
For more information on the different types of heat pumps and planning guidance on air conditioning or A2A heat pumps, see our articles below.
READ:
Retrofitting Heat Pumps Into Houses: A Comprehensive Guide to the Pros & Cons
Do Air Conditioning Units Need Planning Permission?
The first step is to check whether your property has permitted development (PD) rights – a national grant allowing certain types of building work without the need for planning permission. Class G of the General Permitted Development Order (GPDO) is specifically designed for A2W systems and apply to most domestic properties, including houses and flats.
However, if you live on Article 2(3) land – such as a Conservation Area, National Park, Area of Outstanding Natural Beauty (AONB), the Broads, or a World Heritage Site – additional planning controls, known as Article 4 Directions, may apply. You will need to check with your local authority to see if there are any restrictions on your property.
There are specific PD rights governing ASHPs in Conservation Areas and World Heritage Sites – more on these below. However, there are no particular rules for AONBs, National Parks, or the Broads.
PD rights do not apply to listed buildings. If your property is listed, you will need to apply for Listed Building Consent to install an ASHP.
If PD rights apply, the second crucial step is to engage a Microgeneration Certification Scheme (MCS) regulated installer who will conduct a survey of your property and design the heat pump system. This assessment will determine whether the location, size, and performance of the outdoor unit (commonly referred to as the compressor) complies with MCS Planning Standards – a pre-condition for permitted development and the Boiler Upgrade Scheme.
A key factor in locating an ASHP in a built-up area is noise.
MCS document 020 states that an ASHP cannot exceed 42dB at a distance of 1 metre from the centre of a neighbour’s habitable room window, known as the ‘assessment point’. This requirement can make it challenging to find a suitable installation location, as a typical unit produces around 60dB, which may necessitate a significant distance to meet noise limits.
The distance required between the ASHP and the assessment point depends on:
The ideal setup is a quiet unit with only one nearby surface, a solid boundary wall concealing the unit, and no direct line of sight from the unit to the habitable window.
Although a government review has recommended lifting these noise restrictions, they still remain in place at the time of writing. If your ASHP cannot meet MCS noise standards, planning permission will be required.
MCS Planning Standards state that the noise level of an air source heat pump cannot exceed 42dB at 1 metre from a neighbouring window.
Finally, to install a heat pump without planning permission, you will need to meet permitted development guidelines.
In England, Class G of the GDPO allows you to install, alter or replace an A2W heat pump on a residential property without planning permission.
If your property has PD rights, the rules are as follows:
Conservation Areas and World Heritage Sites
If you live in a Conservation Area or World Heritage Site and Article 4 Directions do not restrict heat pump installations, the heat pump cannot be installed:
Permitted development variations elsewhere in the UK
In Scotland and Northern Ireland, the only size restriction on the external compressor is height; it cannot be taller than 3 metres. All other rules apply.
In Wales, the compressor can be up to 1 cubic metre in volume but must be installed at least 3 metres from the site boundary – a significant constraint in a built up areas.
Permitted development rules for air source heat pumps (view of house from the rear).
As noted previously, A2A heat pumps are classified as air conditioning units under PD legislation and usually require planning permission.
Ground source heat pumps (GSHPs) are classed as permitted development. However, planning permission may be needed for excavation works on sites of special scientific interest (SSSI) or in archaeologically sensitive areas. In Northern Ireland, PD rules specify that no part of a GSHP can be within 3 metres of a boundary, and the external unit must not exceed 4 metres in height.
Water source heat pumps (WSHPs) also qualify under PD rights, but a licence from the Environment Agency may be required before installation.
If you're unsure whether your proposed heat pump installation falls under permitted development guidelines, you can seek confirmation from your local authority by applying for a lawful development certificate (LDC).
If your LDC application is deemed 'lawful’, you can proceed with confidence knowing that your plans comply with guidelines. If it’s deemed 'unlawful,' the local authority will detail where your proposals are noncompliant. At this point, you can either modify your plans or apply for planning permission.
Comply with permitted development guidelines whenever you can, as gaining planning permission is usually a lot more onerous.
Understanding the steps outlined above will better prepare you for your heat pump installation.
The information provided in this article is intended for general guidance and educational purposes only. At Designs in Detail, we advise you appoint a skilled residential architect to provide specific expert advice for your project.
About the author
Aron Coates is an architect with over two decades of experience, encompassing projects ranging from the restoration of historic buildings to the design of contemporary homes.
