Air Conditioning Outdoor Unit Noise: What the Law Says and How to Avoid a Neighbour Dispute

The first summer, nobody says anything. The second, the neighbour drops a remark over the hedge. The third, there's a registered letter in the letterbox, then a bailiff's report, then sometimes a judge ordering the outright removal of the outdoor unit — at the expense of whoever installed it.

In the space of two years, outdoor unit noise has become one of the leading causes of neighbour disputes linked to energy renovation. The mechanics are simple: the 5.5% VAT rate on reversible air conditioning has multiplied installations, and those installations are going into suburban housing where homes stand three metres apart, or into building courtyards that behave like echo chambers. A compressor running at 48 dB(A) in an open field bothers nobody. The same compressor between two walls, under a bedroom window, at two in the morning, becomes litigation.

What the law actually prohibits: emergence, not decibels

This is the first misunderstanding, and it wastes an enormous amount of everybody's time. French regulations on neighbourhood noise do not set an absolute decibel ceiling. They work on emergence: the difference between the ambient noise level with the appliance running and the residual noise level without it.

The values are set out in article R. 1336-7 of the French Public Health Code:

Period	Maximum permitted emergence
Daytime (7 a.m. – 10 p.m.)	5 dB(A)
Night-time (10 p.m. – 7 a.m.)	3 dB(A)

On top of these thresholds come correction terms linked to the cumulative duration of the noise: the longer the appliance runs over the period, the stricter the threshold. For continuous operation — which is exactly what an air-to-air heat pump does during a heatwave or in the depths of winter — no tolerance applies: you stay at 5 and 3 dB(A).

Two practical consequences, counter-intuitive but decisive:

1. A quiet appliance can be illegal. On a peaceful country road where night-time residual noise drops to 26 dB(A), an outdoor unit that pushes the ambient level to 31 dB(A) exceeds the night-time threshold. And yet 31 dB(A) is a whisper.
2. A noisy appliance can be perfectly legal. The same unit installed along a boulevard where night-time residual noise sits at 45 dB(A) will produce no measurable emergence at all.

The text adds a common-sense clause: emergence measurements do not apply if the measured ambient level, with the appliance running, stays below 30 dB(A). Below that, no nuisance is deemed to exist.

One point that comes up again and again: the measurement is taken inside the complainant's home, with windows open and then closed, or at the property boundary depending on the case. Not up against the machine's casing. The manufacturer's figure — "47 dB(A)" on the product sheet — is measured at one metre under standardised free-field conditions and therefore tells you nothing on its own.

The other rules that apply at the same time

Noise is not the whole story. An outdoor unit can be challenged on several fronts simultaneously.

Abnormal neighbourhood disturbance. This is a doctrine built up by case law, now written into article 1253 of the French Civil Code by the Act of 15 April 2024. It allows compensation to be obtained even where no regulatory threshold has been exceeded, as soon as the nuisance goes beyond the ordinary inconveniences of living next door to someone. Courts factor in repetitiveness, whether the noise occurs at night, and any marked tonal component — a whistling fan or a deep low-frequency drone carries far more weight than a simple rush of air.

The co-ownership rules. Many flatly prohibit any alteration to the exterior appearance, or require authorisation from the general meeting under the article 25 majority. An installation carried out without a vote can be challenged for ten years, quite apart from any noise issue.

The local town planning plan (PLU). More and more municipalities impose siting rules: minimum setback from boundary lines, a ban on installation on street-facing façades, a requirement to conceal the unit. Some even set a maximum noise level at the property boundary. A visit to the town hall before work starts saves a great deal of backtracking.

Prefectural or municipal orders. Many départements have "noise" orders that additionally regulate hours and noisy activities.

Why your unit makes noise (and which noise, exactly)

An outdoor unit produces three families of noise, and they are not treated in remotely the same way.

Airflow noise

This is the rush of the axial fan. Broadband, fairly high-pitched, it increases with rotation speed. It dominates when the machine is running at moderate load. The good news: it is the easiest to attenuate, because it propagates directionally and a well-placed screen cuts it effectively.

Mechanical compressor noise

Lower-pitched and more penetrating, it often contains a marked tonal component — a dominant frequency that the ear picks out. This is the noise that wakes people up. Recent Inverter models limit it by avoiding abrupt start/stop cycles, but they do not eliminate it. Low frequencies pass straight through lightweight screens and bend around obstacles: a simple wooden panel will do nothing against them.

Structure-borne vibration

The worst case, and the most underestimated. A unit fixed to wall brackets transmits its vibrations into the wall, which then radiates them throughout the structure. The neighbour next door hears a continuous hum inside their home, with the windows closed — without even being able to tell where it comes from. This type of nuisance, known as structure-borne, accounts for a good share of the most serious cases. Rubber anti-vibration mounts fitted between the chassis and its support often solve 60 to 70% of the problem for a few dozen euros.

Getting the installation right solves 80% of the problem

Nearly every dispute I have seen stems from a poor location, not from poor equipment. Here are a few rules that any serious installer follows — and that you should insist on before signing the quote.

• Never blow towards the boundary line. The air leaving the fan should be directed towards your own garden, never towards the party wall or the neighbour's window. An air jet hitting a wall less than two metres away also creates a reflection that can add 3 dB(A).
• Avoid internal corners. A unit placed in a corner formed by two walls suffers a concentration effect: the same appliance can gain 5 to 6 dB(A) compared with installation on a flat façade.
• Keep away from openings. Every doubling of distance in free field removes roughly 6 dB(A). Moving from 2 m to 4 m from a bedroom window already halves the problem to the ear.
• Install at ground level rather than on the wall wherever possible, on a decoupled concrete slab with anti-vibration supports.
• Respect the manufacturer's clearance requirements: a smothered unit recirculates its own air, ramps up, and becomes noisy because it is poorly ventilated.

A good practice is to record the chosen location and the discharge orientation on the quote. In the event of a dispute, that counts as evidence of due diligence.