Methodology
How the sound simulator works
Plays a heat pump recording through a speaker placed where the outdoor unit would go, while a second device measures the sound level around the home.
How it works
The recording is of a real heat pump at full output, which is louder than it usually runs. Visitors set the volume to match the unit they are considering.
The meter averages the microphone signal and adds 94 dB to estimate a sound level. Phone and laptop microphones aren’t calibrated, don’t apply the A-weighting that noise limits use, and adjust their own sensitivity, so readings can be out by 10 dB or more. The meter is most useful for comparing one place with another.
A metre away in the open, a heat pump is about 8 dB quieter than the sound power on its data sheet. It gets about 6 dB quieter each time the distance doubles.
Figures used
Planning noise limit
42 dB(A), 1 m from a neighbour’s nearest window or door
MCS 020, as summarised in DESNZ’s 2023 review of heat pump noise. The 42 dB(A) includes 40 dB(A) of assumed background noise, leaving about 37 dB(A) for the heat pump · Checked 1 October 2026
Drop with distance
About 6 dB each time distance doubles
The inverse-square law, which MCS 020’s calculation is based on · Not re-checked
Level 1 m away
About 8 dB below sound power
The same law, for a unit on the ground away from walls. Each nearby wall adds about 3 dB · Not re-checked
Meter offset
+94 dB
A rough conversion from microphone level, not a calibration · Not re-checked
Limits
- The meter isn’t a sound level meter. For anything that matters, use a calibrated meter or the installer’s MCS 020 calculation.
- Speakers don’t reproduce the low hum of a real unit well, and the recording is of one model.
- Whether a unit meets the planning limit depends on the model, where it goes and what is around it. The installer calculates this.
Last reviewed 1 October 2026. Next review due by 1 April 2027. Try the sound simulator.