Are heat pumps noisy? (UK guide)

The short answer

Modern air source heat pumps are reasonably quiet — comparable to a fridge or a quiet conversation when running normally, with the outdoor fan being the main sound source. A typical unit produces a sound power level in the region of 40 to 60 decibels at the unit, and because sound falls with distance, the level a few metres away is considerably lower. In England, to install under permitted development rights, an air source heat pump must meet an MCS planning noise assessment requiring the sound at the nearest neighbour's habitable-room window to be no more than 42 dB(A). Good siting, anti-vibration mounting and avoiding placement under bedroom windows keep a system quiet. Noise complaints usually trace back to poor positioning rather than the technology itself.

Noise is one of the most common worries about heat pumps. The decibel figures sound abstract, so it helps to translate them into everyday comparisons and explain the rules that govern where a unit can go.

Heat pump noise

Typical sound at unit~40–60 dB
Comparable toA fridge or quiet conversation
MCS permitted-development limit≤42 dB(A) at neighbour's window
Sound behaviourFalls with distance from the unit
Main cause of complaintsPoor siting, not the technology

How loud a heat pump actually is

The main sound from an air source heat pump comes from the outdoor unit's fan and compressor. Manufacturers quote a sound power level, typically in the region of 40 to 60 decibels depending on the model and how hard it is working. To put that in context:

A quiet library is around 30 dB.
A fridge hum or quiet conversation is around 40–50 dB.
Normal conversation is around 60 dB.

Crucially, sound reduces with distance. The figure quoted at the unit is not what you hear several metres away — the level drops as you move away from the source. So the perceived loudness at a window or in a garden is lower than the headline figure, and depends heavily on how far the unit is from where people are.

Decibels are not linear: the decibel scale is logarithmic, so a few decibels' difference represents a larger change in sound than it might seem, and sound falls off noticeably with distance. This is why siting the unit away from windows and seating areas matters so much to perceived noise.

The MCS noise rule and permitted development

In England, installing an air source heat pump often falls under permitted development (so it does not need a full planning application) provided certain conditions are met. One key condition is a noise assessment carried out using the MCS planning standard:

The assessment calculates the sound level the heat pump produces at the nearest neighbour's habitable-room window.
To qualify under permitted development, that level must be no more than 42 dB(A).
The calculation takes account of the unit's rated sound power, the distance to the neighbour and the surroundings.

If the assessment shows the unit would exceed 42 dB(A) at the neighbour's window, the installation may not qualify for permitted development and a planning application could be required, or the unit may need to be repositioned or a quieter model chosen.

Sound level	Everyday comparison	Notes
~30 dB	Quiet library	Below typical heat pump
~40 dB	Quiet fridge hum	Around quieter heat pump output
42 dB(A)	MCS permitted-development limit	Maximum at neighbour's window
~50 dB	Quiet conversation	Higher-output operation, close to unit
~60 dB	Normal conversation	Above typical at-unit level

Indicative comparisons for guidance. Sources: MCS planning standard (MCS 020); Energy Saving Trust. The 42 dB(A) figure is the permitted-development limit at the nearest neighbour's window in England.

Why noise complaints usually come down to siting

When a heat pump is reported as noisy, the cause is rarely the unit itself and almost always where and how it was installed:

Too close to a window: a unit placed near a bedroom window — yours or a neighbour's — puts the sound source where it is most noticeable, especially at night when background noise is low. The MCS noise assessment exists to prevent this at the neighbour boundary.
Vibration transmission: if the unit is fixed directly to a wall or a rigid base without anti-vibration mounts, low-frequency vibration can travel into the building structure and be heard or felt indoors. Proper anti-vibration mounting prevents this.
Restricted airflow: a unit crammed into a tight space or boxed in has to work its fan harder, and reflected sound off nearby surfaces can make it seem louder.
Hard surfaces nearby: sound reflects off walls and fences, so a unit in an enclosed corner can sound louder than the same unit in an open position.
Working hard in cold weather: the unit is loudest when running at full output in cold conditions or during a defrost cycle. A well-sited unit handles these moments without being intrusive.

Because these are installation factors rather than inherent to the technology, they are largely avoidable. A thoughtful installer assesses the position, accounts for the neighbour boundary and uses anti-vibration mounting as standard.

Most noise problems are designed in, not unavoidable: the difference between an unobtrusive heat pump and an annoying one is usually the position and mounting, not the model. Getting the siting right — away from windows, on anti-vibration mounts, with room to breathe — is what keeps it quiet.

What keeps a heat pump quiet

Most heat pump noise problems come from installation rather than the unit itself. The factors that keep a system quiet:

Sensible siting: positioning the outdoor unit away from bedroom windows (yours and the neighbour's) and away from seating areas. The MCS noise assessment helps enforce this.
Anti-vibration mounting: mounting the unit on anti-vibration feet or a suitable base prevents vibration transmitting into the building structure, which is a common cause of perceived noise.
Clearance and airflow: giving the unit room to breathe means the fan does not have to work harder than necessary.
Correct sizing: a well-sized unit running steadily is quieter than an undersized one forced to run flat out.
Quality model choice: manufacturers publish sound data, and quieter models exist for noise-sensitive locations.

Done well, an air source heat pump is unobtrusive. Complaints almost always come back to a unit placed too close to a window or mounted in a way that transmits vibration.

Frequently asked questions

How loud is a heat pump compared to a fridge?

A modern air source heat pump running normally is broadly comparable to a fridge or a quiet conversation — often in the region of 40–50 dB at the unit. Because sound falls with distance, the level a few metres away is lower. The main sound is the outdoor fan, which is most noticeable when the unit is working hard in cold weather.

What is the noise limit for installing a heat pump in England?

To install an air source heat pump under permitted development in England, an MCS planning noise assessment must show the sound at the nearest neighbour's habitable-room window is no more than 42 dB(A). If it would exceed that, the installation may need planning permission, a different position, or a quieter unit.

Will a heat pump keep my neighbours awake?

It should not if it is sited and installed correctly. The MCS noise assessment exists specifically to limit the sound at a neighbour's window to 42 dB(A) for permitted development. Most noise complaints come from units placed too close to a bedroom window or mounted without anti-vibration measures, both of which good installation practice avoids.

Sources & further reading

Figures on this page are typical UK ranges drawn from published sources and depend on your specific home. They are guidance, not a quotation or guaranteed saving.