Advice on how to avoid heat pump noise pollution

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How noisy is a heat pump and how can I limit the noise?
Heat pumps are one of the most popular types of heating in new buildings. In densely built and populated areas, they can sometimes cause discomfort. Some neighbours complain about noise pollution caused by the outdoor units of some air source or ground source heat pumps. How does this happen? What is the noise level of a heat pump? Is there a noise-free air-to-water heat pump?

The topics at a glance:

  • Are air source heat pumps noisy?
  • What are the permitted noise levels?
  • Some tips against heat pump noise
  • Why does a heat pump make noise?

Heat pump heating systems use a technical process to harness environmental energy for heating. Air source heat pumps in particular, which are intended for outdoor installation, can cause noise to neighbours. This is due to the fans and compressors operating in the outdoor units of the devices.

Are modern air source heat pumps really noisy?
The noise level produced by a heat pump is indicated in the manufacturer’s documentation. It gives the values in decibels (A-weighted) or dB(A). The unit represents the sound pressure or noise level according to the internationally standardised A-weighting curve. This acts as a filter with which the sounds audible to humans can be described. At the source of the noise, i.e. directly next to the air-to-water heat pump, the sound emissions are generally between 50 and 65 decibels. As the sound pressure level decreases with distance from the appliance, it is usually less than 45 dB(A) at a distance of three metres, bearing in mind that the noise from the heat pump compressor can be minimised by adding barriers, screens and even noise walls.

Noise comparison: what is the noise level of 45 dB(A)?
Many people are unable to assess whether a sound pressure level of 45 dB(A) is already considered a tone. It is therefore interesting to make a sound scale by comparing sounds. This value, for example, corresponds roughly to the hum of a refrigerator or the sound level of a quiet rain. While normal road traffic in the immediate vicinity generates about 70 dB(A), the sound level of a conversation is about 60 dB(A). The ticking of a clock is 20 dB(A) and the fall of a feather causes just over 0 dB(A). This is the threshold of human hearing, below which perception is impossible.

Difference between sound power and sound pressure
Sound power is expressed in Lw and characterises the sound emission capacity of the source independently of its environment. This sound power (Lw) is measured in the laboratory. It is the value that allows direct comparison between devices.
The sound pressure is expressed in Lp and is defined as the acoustic quantity perceived by the human ear and measured by the sound level meter. For a given source, the sound pressure (Lp) depends on the installation environment and the distance at which the measurement is made.

Heat pump noise: what should be taken into account?
When looking at the noise levels of different air source heat pumps, the main thing to check is the noise thresholds. The values can only be compared if they refer to the same distance from the heater and the same temperature conditions. In addition, certain installation conditions can increase noise pollution. This is the case for example under awnings or between two walls.

What is the permissible noise level of a heat pump?
The noise level of a heat pump heating system depends largely on the time of day and the area of residence. As a general rule, units can be louder during the day than at night. The noise conditions determined by the place of residence should not be underestimated, as they differ significantly between industrial, urban and residential areas.

The following table shows the thresholds that should not be exceeded in cities, on roadsides or in quieter areas.

What do the regulations say about heat pump noise?
The regulation of neighbourhood noise is governed by the decree of 31 August 2006 and standard NF S 31-010. The nuisance is defined by the notion of emergence, i.e. the difference between the sound pressure level measured when the appliance is stopped compared to the level measured when the appliance is in operation at the same location. Emergence measurements must be taken at the property line. In the case of buildings, these measurements must be made in the living areas with the windows open and with the windows closed.
The regulations differentiate between daytime and nighttime emergence:

During the day (7am – 10pm), maximum permitted deviation of 5 dB(A)
At night (10 p.m. – 7 a.m.), maximum permissible difference of 3 dB(A)

If the noise nuisance from a heat pump exceeds these thresholds and can be observed within a given perimeter around your home, then corrective work will be necessary. Please note that this refers to the sound pressure level measured in living areas, such as living rooms or bedrooms.

Noise pollution from my neighbour’s heat pump: what can I do?
If you are affected by noise pollution from your neighbour’s heat pump, we recommend that you first contact your neighbour directly. Discuss together what measures could be taken to reduce the sound pressure level in your bedrooms or living rooms. If this does not help, contact the local council. As a rule, expert advice is also required.

Simple measures against air-source heat pump noise
The first priority is always to choose a suitable location for the heat pump. If the installation is not optimal or if conditions have changed over time, simple measures can be taken to limit the noise of an air-to-water heat pump, as mentioned below:

Quiet night-time operation: storage tanks and surface heating systems such as underfloor heating store heat in the building. If these systems are available, the heat pump output can be reduced at night, which also allows for quieter operation. A hot water storage tank can also be used to delay water heating until the early hours of the morning for quieter operation at night.
Install a sound insulation box: This is a housing that manufacturers offer as an add-on for air source heat pumps and some heat pump outdoor units. This reduces noise emissions by insulating the noise.
Hedges and screens: Dense evergreen hedges between the noise source and neighbouring houses are also useful. Like sound barriers (or heat pump noise barriers), they reduce noise emissions.
Moving the heater: If the housing estate consists of various town houses, you can have the heat pump outdoor unit moved to the street side. This way, the noise emissions are drowned out by the city noise and the neighbours are less affected by the noise. Vibration dampers that decouple the heat pump heating from the building structure are also useful in this context.
Summary of solutions for reducing heat pump noise
If you are affected by noise from your neighbour’s heat pump, it is a good idea to start by discussing this with your neighbour, as there are solutions available to reduce heat pump noise. Report the problems to your neighbour and work together to find a solution. Adjusting the settings, installing a soundproofing cover or putting up a hedge are usually simple to implement and can lead to a quick improvement.

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