Dispelling Myths on Heat Pump Noise

A topic under exploration by Homebuilding and Renovating magazine is potential complaints from neighbours about your air source heat pump (ASHP).

So let’s explore the topic in a balanced way:

It is a common concern for homeowners considering an air source heat pump but is it justified in 2025? While all heating systems produce some noise, the location and type of sound from an ASHP are distinctly different from a traditional gas or oil boilers’ flue. It sometimes seems to be that we’re tolerant of familiar technology and intolerant of perceived ‘new’ technology.

The Sound of an Air Source Heat Pump

Air source heat pumps are installed outside a property, where a fan draws in air to extract heat. The main sources of noise are the compressor and the fan, which produce a low hum or whirring sound. The noise level of a modern ASHP typically ranges from 40 to 60 decibels (dB), this is comparable to a refrigerator, a quiet conversation, or a running stream.

The noise level can increase on colder days when the unit has to work harder to extract heat, but of course neighbours a likely to have their windows closed on these colder days.Also, advancements in technology mean that modern units are significantly quieter than older models. In the UK, regulations are in place to prevent noise nuisance. For installations that don’t require planning permission (those covered under Permitted Development) the noise from the heat pump must not exceed 42 dB at a neighbor’s habitable room (like a bedroom window). This is a very strict limit, meaning most well-sited and correctly installed units will be barely noticeable to neighbours.

The Sound of a Gas Boiler Flue

Gas boilers are installed inside the home. The flue pipe expels combustion gases outside. Under some circumstances this can be noisy if close to a neighbours house. The boiler flue can become significantly noisier if there is a fault. A faulty boiler can create loud, unusual noises such as banging, gurgling, or a whistling “kettling” sound, which could be more noticeable to others.

The Sound of an Oil Boiler Flue

An oil boiler’s flue can produce a range of external noises that may annoy neighbors, primarily due to the combustion and air movement within the system. The most common sounds are:

Whooshing or roaring: This sound is typically generated by the rush of hot combustion gases being expelled from the flue. It can be particularly noticeable during boiler startup and shutdown, and can be worsened by a strong wind or a partially blocked flue.

Vibrating or humming: This is often caused by the boiler’s fan or pump, with the vibration traveling through the wall and into the flue pipe, which then acts like an amplifier. A loose component or a faulty fan motor can make this noise more prominent.

Whistling or “kettling”: Although this sound is usually associated with internal boiler issues like limescale buildup, the noise can be loud enough to be heard outside, particularly if the flue is close to a neighbor’s window. It’s a high-pitched sound created by water boiling inside the heat exchanger.

Factors that Increase Flue Noise

Several factors can make the external noise from an oil boiler flue more disruptive to neighbors:

Flue Location: If the flue is positioned too close to a neighbour’s window, or a shared alleyway, the sound will be much more noticeable. Building regulations in the UK specify minimum distances to prevent such nuisance, but older installations may not comply.

Acoustic Amplification: The flue pipe and the wall it’s mounted on can act as a soundboard, amplifying the vibrations from the boiler itself. A poorly secured flue can also rattle against the wall, creating an irritating rattling sound.

System Faults: As noted above, unusual noises often indicate a problem with the boiler. A misaligned burner, a faulty fan, or a blockage can all lead to louder-than-normal operation. Regular maintenance is crucial to ensure the boiler runs as quietly and efficiently as possible.

Wind and Weather: Strong winds can interact with the flue terminal, creating a howling or whistling sound.

Conclusion

Many people living in rural areas, considering installing an ASHP are preoccupied with the potential of noise nuisance.

Whilst it is certainly worth ensuring that the required noise assessment is carried out professionally, most fears are groundless.

Very few rural locations are as free from noise as residents perceive. Often there are noisy oil boiler flues that have been tolerated for years.

An ASHP produces more noise in the depths of winter when windows are closed. In the Summer when the unit is replenishing hot water there is likely to be a carcophony of lawn mowers, chain saws and birds singing that drown out the gentle hum of the heat pump fan.