Heat pumps can cause noise complaints from neighbours. The person who has installed the heat pump to do the right thing to mitigate CO2 emissions and to reduce power consumption and bills may then have to contend with noise complaints. This may happen even when the headline noise level planning requirements have been met.
Unfortunately, we cannot provide specific help to private individuals. The INVC is a commercial organisation and we do not have the resources - we have to charge! However, the following guidance should allow you to solve most problems yourself or in conjunction with the Local Authority Environmental Health Officer (EHO).
What to do if you have noise complaints about your heat pump?
Current heat pump noise specifications are based on the overall noise level measured in dB(A). This is often seriously inadequate as it only addresses part of the issue. It does not take into account the low-frequency hum often produced by heat pumps. Nor does it take into account vibration that may be transmitted into the building that is then heard as a low-frequency humming noise. Don't guess! Use the following diagnostic process to understand the problem.
Step 1: diagnostic process
The first step to eliminate the complaints is to understand the nature of the noise that is the cause. There are 3 possibilities:-
- broadband noise measured as dB(A). This is the single figure overall noise level provided by the supplier. However, measuring dB(A) means that low frequency noise components have been filtered-out, posing a problem if there are low-frequency noise components from the pump.
- airborne low-frequency tonal noise from the fan and/or from the compressor, the "hum".
- structure-borne vibration from pipes and/or the mounted heat pump that cause walls or joists to vibrate and that is then heard inside as a low-frequency hum. This can be diagnosed by comparing the noise with the window open and shut - there won't be miuch difference if the problem is vibration.
- structure-borne vibration from mounting the heat pump on a flat roof. The pump has been mounted on a very large loudspeaker. Conventional anti-vibration mounts are often not suitable for this type of installation as they are designed for floor mounting.
Go through the following process to determine which of the above is the dominant issue. Be aware that heat pump noise varies considerably with load. They are much noisier in very cold weather.
- Ask: ask the complainant about the nature of the noise about which they are complaining. This may or may not provide useful information as many people struggle to describe noise in words. Specifically, ask if they hear a hum or drone. In addition, ask them where and when the noise is worst - outdoors, indoors, at night etc. Note that listening to and assessing heat pump noise near the pump will not usually give you a useful impression of the problem.
- Listen: if at all possible, listen to the noise yourself at the worst complaint location(s) and try to describe it to yourself as above.
- Analyse: download a free noise spectrum analysis app to your smartphone (there are many, for example https://www.keuwl.com/SpectrumAnalyser/ for android). Set the maximum frequency range to around 1000Hz and analyse the noise signature at the worst complaint location. If there are large peaks at particular frequencies (see example below), then there are tones (hum or drone). More tonal noise analysis information here >
Heat pump noise analysis example
In this example, as a result of complaints from a neighbour, the owner spent >£4k on an acoustic enclosure that had no effect on the complaints. Whilst the enclosure reduced the overall dB(A), it did not reduce the cause of the complaints which was a hum at 58Hz. This noise signature narrow band frequency analysis from video clips provided by the owner clearly shows that the complaint was not about the dB(A), but about a very low frequency hum at 58Hz that could not be attenuated by an enclosure.
If the above process had been followed, it would have been obvious that the enclosure would not have worked.
The lack of any diagnostic process to determine the characteristics of the heat pump noise that are the cause of the complaints is extremely common. This leads to time and money being wasted on the installation of ineffective noise control measures (Environment Agency and EHO surveys indicate that 95% of noise consultant reports are inadequate).
Step 2: evaluate the heat pump noise attenuation options
The optimum noise control solution depends on the nature of the noise problem as diagnosed above.
- Broadband noise measured as dB(A). Depending on the site geometry, simple acoustic barriers or an off-the-shelf acoustic enclosure may well be sufficient. Even DIY enclosures (marine plywood and acoustic absorbent foam or rockwool) can be very effective, but be careful not to compromise the airflow.
- Airborne low-frequency tonal noise. The acoustic enclosures or barriers that are often installed are rarely effective due to simple physics. If it is the fan, then the only real solution is aerodynamic noise control (for which we would have to charge) or a very carefully designed, non-standard enclosure/silencer. If the problem is the compressor, then the solution is improved vibration isolation and/or damping of the heat pump casing.
- Structure-borne vibration. Ensure that the compressor inside the casing is properly vibration isolated with no hard links (you should be able to wobble the compressor quite easily) and with flexible connections to the pipes. In addition, if the pipework into the building is hard mounted to structures such as joists (or even the brickwork in some cases), this will transmit pressure pulsation vibration that will then be heard as noise. If the pump has been mounted on a flat roof, then make sure the pump is above a joist and mounting it on a large paving slab that is then isolated from the roof with 50mm or more of rockwool may be a solution.
More on the optimum heat pump noise control methods here >
Step 3: contact your local EHO
Your neighbour may already have done this! They will have the instrumentation to evaluate a complaint, but be aware that they will often only consider the overall dB(A) - which gives you a problem if that is not the primary cause of complaints. Some will also be able to carry out the diagnostic measurements and analysis described above, but we would recommend that you should already have carried out your own evaluation as above.
Hope you find this useful...
