A heat pump that is correctly sized and correctly placed is not noisy. What you hear from the outdoor unit is the hum of the compressor and the sound of air moving through the fan; on a modern unit running at part load, a few metres away, that sound comes close to the background level of a quiet room. The indoor unit has no compressor, so it is far quieter still. How much you actually hear depends as much on the installation as on the unit: the distance to the nearest window, the walls behind it, whether vibration reaches the building and how fast the unit runs at night.
This article explains how to read the dB(A) figures in a catalogue, lists the sound levels of AD units and covers what to look at when choosing a place for the outdoor unit. If you want to know how the machine works first, see what a heat pump is and how it works.
What dB(A) means and how to read it
Sound level is measured in decibels (dB), and the scale is logarithmic. An increase of 10 dB means ten times the sound energy, which the ear perceives as roughly twice as loud. An increase of 3 dB means the sound energy has doubled. Put two identical units side by side and the combined level is 3 dB higher than one unit, not 6 dB.
The (A) stands for A-weighting. The human ear is less sensitive to very low and very high frequencies than to the frequencies of speech. An A-weighted measurement imitates that sensitivity and brings the result closer to what we actually perceive, which is why heat pump, air conditioner and household appliance catalogues give their figures in dB(A).
Some approximate reference levels: a quiet bedroom at night 25–30 dB(A), a whisper around 30 dB(A), a quiet office 40 dB(A), normal conversation at one metre 55–60 dB(A).
Sound power and sound pressure: two different figures
Catalogues use two different quantities. The most common mistake is to compare one with the other as if they were the same thing.
- Sound power level (LWA): the total sound energy the unit emits. It does not depend on distance or surroundings; it is a property of the unit itself. The sound figure on the European energy label is sound power.
- Sound pressure level (LpA): the sound that reaches the ear at a given point. It is always stated with a measuring distance (for example "at 1 m") and changes with the reflections around the unit.
For the same unit, sound pressure is always lower than sound power. For a unit standing on the ground with open space around it, the sound pressure at 1 metre is about 8 dB below the sound power. So a unit listed at 60 dB(A) sound power in one catalogue and another listed at 52 dB(A) sound pressure in a second catalogue may be making exactly the same noise. When you compare offers, make sure you are comparing the same quantity at the same distance.
Sound levels of AD units
Our technical tables give the sound pressure at a distance of 1 metre. Where a range is given, the value depends on the operating state: the lower figure applies with the compressor and fan at low speed, the upper figure at full load.
- Poyraz series: 22–32 dB(A) for the Poyraz 12, 35–48 dB(A) for the Poyraz 14 and Poyraz 16. The 12, 14 and 16 kW models of the Boran and Vaha series have the same values.
- V series outdoor unit: 43–54 dB(A) for the V20 and V24.
- W series outdoor unit: 43.6 dB(A) for the W28; 43.7 for the W35 and W40; 46.6 for the W45, W50 and W56.
- HİD / HİT wall-mounted indoor unit: 18 dB(A) for the HD8, HD10 and HD12, 23 dB(A) for the HD14 and HD16.
- HİDRA indoor unit with tank and HİDREM: 22 dB(A) for the 8, 10 and 12 kW models, 34 dB(A) for the 14 and 16 kW models.
In the V and W series the compressor runs in an insulated compartment with a silencer. In the W series the values rise only slightly with capacity.
Distance and reflections
In open space, sound drops by about 6 dB every time the distance from the source doubles. An example: the V20's full-load value of 54 dB(A) is measured at 1 metre. With nothing in the way you can expect about 48 dB(A) at 2 metres, 42 at 4 metres and 36 at 8 metres. This is a rough calculation: right next to the unit the sound falls off more slowly, while a wall or a dense hedge in between gives an extra reduction.
Reflecting surfaces work the other way. Compared with an open spot, a unit placed against a wall sounds about 3 dB louder, and a unit in a corner where two walls meet about 6 dB louder. A narrow light well or an enclosed courtyard reflects the sound again and again; these are the worst places for an outdoor unit.
When several units run together, their levels do not add up arithmetically; they combine logarithmically. In the W series, large demands are met by combining several units: two W45 units side by side give a combined level of about 49.6 dB(A), three W45 units about 51.4 dB(A).
Where to put the outdoor unit
- Away from bedroom windows: the distance to the nearest bedroom window and to the neighbour's facade matters more than the unit's own sound level.
- Fan outlet not facing the neighbours: most of the air and sound leaves through the front of the unit; turn the front towards the garden or a blank facade.
- Keep the air inlet and outlet clear: a unit with a blocked front, or one that draws its own discharge air back in, has to run its fan faster; both noise and consumption go up.
- Avoid corners and narrow gaps: the reflections described above add a few decibels for nothing.
- Ground mounting where possible: a solid concrete base passes far less vibration into the building than a wall bracket.
In housing estates and apartment blocks, the building's management rules and local regulations may limit where the outdoor unit can go. This needs to be settled at the design stage, before the unit is chosen.
Vibration: the part of the sound that enters the building
When a unit is rigidly fixed to the building, the vibration of the compressor and fan travels through walls and floors. This structure-borne sound is low in frequency and has no obvious source, which makes it more disturbing than airborne sound.
- The unit sits on rubber or spring vibration isolators (anti-vibration feet).
- If it is wall-mounted, the bracket is fixed to a load-bearing wall with dampers between bracket and unit. Lightweight partition walls next to a bedroom are not suitable.
- Pipes are not tightly embedded where they pass through the wall; rubber-lined clamps and flexible connections on the water lines stop vibration from travelling along the pipework.
Night-time and part-load operation
A heat pump spends most of its time below full load. With an inverter compressor the capacity is adjusted continuously; on a mild night the unit runs at low speed, close to the lower end of the range in the table. The start-up noises of older on/off units also become rare. In the Poyraz, Boran, Vaha, V and W series the compressor is DC inverter and the fan is BLDC.
Many heat pumps have a night mode (quiet mode) that limits compressor and fan speed during set hours. The price is somewhat lower capacity during those hours; in a well-insulated building with underfloor heating, this hardly shows in the indoor temperature.
The choice of capacity affects noise too. An undersized unit runs flat out on cold days, at the top of its range. A correctly sized unit stays mostly at part load even on the coldest days. We explain how capacity is worked out in our article on choosing a heat pump.
There is one more sound you may hear in winter: defrosting. In cold, humid weather the coil of the outdoor unit ices up, and at intervals the unit reverses its cycle to melt the ice. During this the fan stops, there is a short hiss as the valve switches, and steam may rise from the coil. This is part of normal operation. In the V and W series the ejector circuit and the control system delay defrosting, so the unit defrosts less often.
The indoor unit
In the indoor unit, the sound comes from the circulation pump and from water flowing through the pipes. That is why the values above stay in the 18–34 dB(A) range. Placed on a utility balcony or a corridor wall (the wall-mounted HİD / HİT), or in a plant room or pantry (the HİDRA and HİDREM with tank), the indoor unit cannot be heard from the living space.
For your project
If you already know where the unit will go, include it in your quote request: the distance to the nearest window and to the neighbouring facade, whether the unit will stand on the ground or hang on a wall, and any rules of the estate. We propose the model and its placement together with that information. The sound levels of the models are in the technical tables on our heat pump product pages; for a quote, use the contact form.
