How much noise does a heat pump make?

An air-to-water heat pump extracts heat from outdoor air. A fan pulls air through the outdoor unit, and inside a compressor squeezes the refrigerant. Those two parts make the sound: a soft whoosh from the fan and a low hum from the compressor. It is a constant, even sound, not a peak noise like a slamming door.

How hard the unit works determines how much you hear. On a mild day it runs gently and you hear little from a few metres away. On a cold winter day, when heat demand is high, the fan spins faster. Defrosting (the unit clearing ice off its own fins) also adds some sound temporarily. Indoors you hear next to nothing from a well-placed outdoor unit.

Since April 2021 the Dutch government sets a noise requirement for outdoor heat pump and air-conditioning units at homes; the rule now lives in the building decree (Besluit bouwwerken leefomgeving, Bbl). An outdoor unit may cause at most 40 decibels at the boundary with an adjacent residential plot, and at an openable window or door of a home, as explained by the government's Informatiepunt Leefomgeving. If the unit has a separate evening and night mode, a correction applies during the day (7:00 to 19:00), effectively allowing 45 decibels in daytime.

Good to know: the limit does not apply vaguely somewhere in the garden but precisely at the plot boundary and at the neighbours' windows and doors. Forty decibels is comparable to a quiet residential street at night; softer than a normal conversation. The installer must show in advance that the setup meets the requirement; an official calculation tool exists that factors in distance, screening and reflection.

Sound drops off quickly with distance: every doubling of the distance makes a noticeable difference. The biggest gain is therefore the spot itself: not right on the plot boundary, not straight under the neighbours' bedroom window, and the fan outlet not aimed at the neighbours. A wall or fence between unit and neighbours dampens further, though a hard wall directly behind the unit can also reflect sound; a good installer weighs that in.

Vibration dampers under the unit help too (so the hum does not travel through the facade into your home or the neighbours'), and where needed a sound-dampening enclosure. Modern units also have a quiet mode for evening and night: the unit deliberately runs slower. That costs a little capacity at exactly the hours you need less heat anyway.

During the survey we look not only at your fuse box and heat demand but explicitly at the placement: distance to the boundary, the position of bedroom windows (yours and the neighbours') and the surface. We run the noise requirement on that, so the permit check and the neighbours hold no surprises. Unsure whether your situation fits? Put it to us or first read the heat pump page. How the heat pump compares to your current boiler is covered in heat pump vs gas boiler.