When a sound source is set into vibration, it spreads out in waves. Each sound wave displaces the surrounding air, creating an audible fluctuation in air pressure - in other words, a noise or sound. Please note that the relationship between the sound pressure and the volume that our hearing can perceive is not linear.

The measured variable for air pressure fluctuations is Pascal. As this is a logarithmic variable, we use the internationally standardized sound pressure level, given in decibels dB(A), for simpler representation.

f the air pressure fluctuates greatly, we perceive the noise as loud. The hearing threshold is 0 B(A) and the pain threshold begins at around 120 dB(A). The sound pressure decreases with distance from the sound source. If the distance is doubled, the sound pressure level drops by 6 decibels. An increase of 10 decibels corresponds approximately to a doubling of the (perceived) volume.

Due to the central role of heat pumps in climate-friendly heating, their noise level is increasingly becoming a topic of conversation. Since in most cases the neighbors' property line is only a few meters away, we occasionally read about complaints and even court cases. Noise is always perceived subjectively. So you can't talk anyone out of a supposed or actual noise nuisance caused by a heat pump. The best solution to avoid disputes from the outset is therefore to entrust the installation of your heat pump to a professional specialist company that is familiar with the limit values for noise pollution and acoustic requirements.

All manufacturers include the sound power level according to DIN EN 12102-1 for day and night operation in their product data. It is measured directly at the sound source and provides you with an initial point of reference for comparing heat pumps. However, the decisive factor is always which sound immissions reach the neighbor. In the construction industry, the so-called rating level Lr is used as a parameter for this. It is calculated according to a standardized procedure and should always be lower than the applicable limit values.

Another term comes up in this context: tonality. In acoustics, it describes the effect that a single tone or a whistle stands out from a monotonous noise. When planning the installation location of heat pumps, the sound pressure level is therefore often multiplied by 3, in some cases even 6 decibels, in order to obtain the actual rating level. Good to know: For the modern air/water heat pumps from alpha innotec, there is no need to include a surcharge for tonality, as no individual tones are audible due to their acoustic optimization.

The limit values, more precisely formulated, the guide values for outdoor immissions, are regulated in the Technical Instructions for Protection against Noise – TA noise. The values apply to built-up areas in front of the open window of rooms requiring special protection, such as bedrooms and children's rooms. In the case of undeveloped areas, a building with rooms requiring protection that may be erected in accordance with building regulations is assumed. A difference of 3 decibels means a doubling or halving of the sound energy.

The noise level is a particularly important issue with air/water heat pumps for outdoor installation. Although modern air/water heat pumps are very quiet in operation, they cannot operate completely without moving parts that can cause noise - just like a refrigerator, which is based on the same, albeit reversed, operating principle. In an air/water heat pump, the fan draws in the outside air and blows it past the evaporator pipe system in which the refrigerant circulates. The refrigerant absorbs the air temperature. The air is compressed in the compressor and the refrigerant continues to heat up. These switching cycles can generate an audible noise level, especially at night. When planning and installing your air/water heat pump, you therefore need to consider a few things together with your specialist partner.

• The most important thing is the right installation location. Your heat pump should be installed as far away as possible from rooms that require protection and as freely as possible. Hard walls, floors and corners near your heat pump can reflect sound and cause the noise level to be higher than calculated.
• The structure-borne sound of the heat pump can also be transmitted into the house via pipes, lines and walls. This can be prevented with suitable sound decoupling measures.
• You can also prevent sound transmission within the house. Acoustic sealing of the plant room or a sound-absorbing floor on which the heat pump is mounted are not a must, but you can prevent the possible spread of operating noises in any case.
• Choose a heat pump with the option of night mode. Our modern air/water heat pumps, such as the Hybrox high-temperature heat pump, are barely audible in night mode.

The easiest way to reduce the noise level of the heat pump even further after commissioning is to install a sound insulation cover.

Acoustically optimized and correctly planned heat pumps are whisper-quiet from a distance of around one metre. The noise level of your heat pump during operation depends on several factors. The most important are the measured values for the sound power level, the installation location and the installation situation, the sound level, the rating level and the applicable immission guide values. For more in-depth information, we recommend the Sound guide (status 2019) from the German Heat Pump Association (Bundesverband Wärmepumpe e.V.)