Works out the sound pressure level at a neighbour's window and whether it clears the permitted development limit.
Most of the form is filled in already with figures that give a sensible answer. Adjust what you know and press the button.
Calculate the sound pressure level an air source heat pump produces at an assessment position, and whether it meets the 37 dB(A) permitted development noise limit, using the method in MCS 020.
The formula is Lp = Lw + 10 log(Q / 4.pi.r^2) - Ab.
Lw is the A-weighted sound POWER level of the unit from its product fiche, energy label or the MCS product database. This is not the sound pressure level, which is a smaller number that already has a distance built into it; confusing the two produces an answer that is wrong by about twenty decibels. The figure for low noise mode must not be used.
Q is the directivity factor, from the count of reflecting surfaces within one metre of the unit that extend at least a metre past it in two or more directions. The ground counts; vegetation does not. One surface gives Q=2, two gives Q=4, three gives Q=8. More than three cannot meet MCS 020 at all.
r is the straight-line distance in metres to the assessment position, which is a window or door of a habitable room in a NEIGHBOURING property, at any floor. Every affected position must be checked separately, and the nearest is not always the worst.
Ab is the barrier attenuation. Fences with gaps, and vegetation of any kind, count as no barrier.
Where several units serve one position, list them all and they are combined logarithmically.
The same calculation answers on
POST /api/calculators/heat-pump-noise
and as the MCP tool heat_pump_noise.
How to call them.
Most air source heat pumps are installed under permitted development, and one of the conditions is a noise calculation. This is what the calculation does and what fails it.
Short answers on what needs permission, what needs notifying, and which documents will still matter in ten years.