Heat Pump Noise: Planning Rules and the 42 dB(A) Standard Explained

Noise is one of the most common concerns homeowners raise before installing a heat pump. The good news is that modern air source heat pumps are significantly quieter than older models, and most installations fall comfortably within permitted development rights — meaning no planning application is needed. The bad news is that there are specific noise rules that some properties fail, and the permitted development rights have conditions that are not always explained clearly by installers.

Do heat pumps need planning permission?

In England, air source heat pumps are classified as permitted development under the Town and Country Planning (General Permitted Development) Order 2015 (as amended). This means they can be installed without submitting a planning application, provided they meet all of the following conditions:

• •Only one heat pump is installed on the property
• •The unit is not installed on a wall or roof facing a highway
• •The unit is at least one metre from the property boundary
• •The noise level does not exceed 42 dB(A) at one metre from any neighbour's window or door
• •The property is not in a conservation area, national park, or Area of Outstanding Natural Beauty (AONB) — if it is, additional restrictions apply
• •The installation follows MCS 020 planning standards

In Wales, similar permitted development rights apply under the Town and Country Planning (General Permitted Development) Order 1995 (as amended). Scotland has its own planning framework — consult your local authority or MCS installer for Scotland-specific rules.

The 42 dB(A) noise standard explained

The 42 dB(A) limit is measured at one metre from the nearest neighbour's habitable room window or door. For context, 42 dB(A) is approximately the noise level of a quiet conversation or a residential street at night. Most modern air source heat pumps produce 45–55 dB(A) at one metre from the unit itself, but the noise level falls with distance according to the inverse square law — roughly 6 dB for every doubling of distance.

Whether a specific installation meets the 42 dB(A) limit depends on the distance to the neighbour's window, any reflective surfaces (walls, fences) that could amplify sound, and the noise output of the specific unit at the proposed siting location. MCS 020 requires installers to assess compliance as part of the installation process.

When the noise limit causes problems

Properties where the 42 dB(A) limit is difficult to meet include terraced houses with small rear gardens, semi-detached properties where the garden boundary is close to the neighbour's habitable windows, and flats or apartments where an outdoor unit would be sited on a balcony or communal area near other residents.

In these cases, installers have several options: choosing a quieter unit (some models are specifically designed for noise-sensitive installations, rated as low as 40 dB(A) at one metre), siting the unit on the opposite side of the property from the neighbour's windows, installing acoustic barriers (purpose-built enclosures that reduce noise transmission without restricting airflow), or — in rare cases — concluding that an air source unit is not suitable and recommending a ground source system instead.

Conservation areas and listed buildings

Properties in conservation areas, national parks, AONBs, or World Heritage Sites lose the standard permitted development right for heat pumps in most cases, and a full planning application is required. Listed buildings require listed building consent in addition to planning permission. If your property falls into any of these categories, contact your local planning authority before commissioning a survey — the planning process can add 8–12 weeks and a planning fee to the project timeline.

That said, planning permission for heat pumps in conservation areas is routinely granted when the unit is sited sensitively — typically at the rear of the property, out of sight from public areas, and with a noise assessment demonstrating compliance.

Flat roofs and wall mounting

Most air source heat pumps are ground-mounted, but they can also be wall-mounted or roof-mounted where ground space is limited. Permitted development rights still apply to wall and roof mounting, provided the unit does not face a highway and all other conditions are met. Wall mounting requires structural assessment to ensure the wall can bear the unit's weight (typically 80–150 kg for domestic units), and vibration isolation mounts are essential to prevent structure-borne noise transmission into the building fabric.

Checking compliance before installation

Your MCS-certified installer must assess noise compliance as part of the MCS 020 process before installation. They should provide you with a written assessment confirming the installation meets permitted development requirements. If you are concerned about neighbour relations, it is worth sharing the noise assessment with neighbours before work begins — a proactive conversation is far better than a noise complaint after installation.