Frequently Asked Questions

Often not: a ground-mounted outdoor unit is generally permit-free if it is no taller than 1 metre, no larger than 2 m² and not on the front facade or street side. Placement on the roof, on the front facade or on a listed building usually does require a permit, and municipalities may add local rules — check your situation via the Dutch online permit portal (Omgevingsloket). Note: a permit-free unit must still meet the 40 dB noise limit; permit-free does not mean rule-free.

The sound power (LwA) of modern air-to-water heat pumps typically ranges from 48 to 65 dB(A); hybrid heat pumps tend to be on the quiet side due to their smaller capacity, and silent mode shaves off a few more dB. The value is mandatory on the energy label and product fiche. The difference matters more than it seems: every 5 dB quieter at the source nearly halves the distance needed to the boundary.

The municipality (or the environment service) can enforce, usually after a neighbour reports it or files an enforcement request. It can commission a calculation or measurement and, on exceedance, impose measures under penalty payments: from activating silent mode or adding a screen or enclosure up to, in the last resort, relocating or removing the unit. Making and keeping a calculation in advance puts you in a much stronger position in such a dispute.

A decibel app gives a rough indication at best: phone microphones are not calibrated, do not measure a standardised dB(A) value at the correct assessment point and cannot exclude ambient noise. The legal test is in fact not a measurement but a calculation following the official method — exactly what this tool does. In a formal dispute, only a calculation or measurement by a certified acoustic consultancy or the environment service counts.

The 40 dB limit concerns airborne sound at the assessment point. A hum caused by vibrations travelling through the foundation, wall bracket or roof structure (structure-borne sound) is not assessed separately under that limit, but can still constitute nuisance under the duty of care or civil neighbour law. The fix lies in the installation: rubber vibration dampers or a decoupled mounting frame belong in every professional installation. If the unit produces an audible pure tone, the tonal penalty K1 also counts in the assessment.

Not mandatory, but it makes a big difference. Without silent mode, your heat pump must meet the 40 dB(A) limit both day and night. With silent mode, the unit may produce up to 45 dB(A) during the day — 5 dB more, which corresponds to nearly double the sound power. Most modern heat pumps have this feature.

The directivity factor Q describes how sound spreads from the outdoor unit. On an open roof (Q=2), sound spreads as a half-sphere. Against one wall (Q=1), sound is concentrated into a quarter-sphere — making it louder toward the neighbors. In a corner with two walls (Q=0.5), concentration is even stronger. The tool calculates Q automatically based on walls within 2.5 meters.

No, this tool calculates noise from a single outdoor unit. This is in accordance with the statutory system, which sets requirements per individual outdoor unit and does not account for multiple units and cumulation. For situations with multiple units, advice should be sought from an acoustic specialist.

Yes, a closed garden wall or screen on the property boundary can reduce noise by 5 dB (the screen correction K_sch). Requirements: the screen must weigh at least 10 kg/m² (e.g. a half-brick wall or 4mm glass), be fully closed without gaps, and you must also verify compliance at higher windows/doors of neighboring houses.

Place the outdoor unit as far from the property boundary as possible. Every doubling of distance reduces noise by 6 dB. Preferably do not place the unit in a corner (this amplifies sound), but against a single wall. A garden wall or screen between the unit and the boundary can reduce noise by 5 dB.

Sound power level (LwA) is the total sound energy emitted by a heat pump — this is listed on the manufacturer's spec sheet. Sound pressure level (LpA) is what you actually hear at a certain distance. The calculator computes the LpA at the property boundary based on the LwA, accounting for distance, screening and reflections.

According to the Dutch Building Works Decree (Bbl, articles 4.107(2) and 4.108(3) — formerly Building Decree 2012, articles 3.8(2) and 3.9(3)), the noise level of an outdoor unit at the property boundary may not exceed 40 dB(A) during evening and night (19:00 - 07:00). During the day (07:00 - 19:00), the limit is 45 dB(A), but only if the unit has a separate silent mode for the evening and night period.

The tonal penalty K1 is a surcharge in dB added to the sound power level if the heat pump produces audible pure tones (whining, humming, droning). The value must be obtained from the supplier. Tonal noise is perceived as more annoying, hence this penalty. K1 may differ between day and night periods.

When placed on the roof, the tool calculates screening by the roof edge. Important: you must always also check at openable windows and doors of neighboring houses, as these may not be screened. Use the receiver positions in the tool for this. For pitched roofs, the gutter height is used as reference.

Use this calculator to determine the maximum allowable sound power level (LwA + K1 - D_enclosure) for your situation. Then ask your supplier for the maximum sound power level and tonal penalty (K1). If your unit's effective LwA is lower than the calculated maximum, you meet the requirements.

The margin is a safety buffer that accounts for uncertainties in the design and measurement process. The recommended value is 3 dB, the minimum is 2 dB (per NPR 5070 and NPR 5086). The margin is subtracted from the calculated maximum allowable sound power level. A higher margin gives more certainty that you will meet the requirements in practice.

Yes, the noise requirements of the Bbl apply to all outdoor installations for heating or cooling. This includes both air-to-water heat pumps and air-to-air heat pumps (air conditioners). The limit values and calculation method are identical.