The quietest OCHSNER
Air heat pumps

Anyone wanting to compare heat pumps should understand that there are two different physical quantities, both expressed in decibels, but making completely different statements.

The sound power level describes the acoustic power emitted by a heat pump. This value is measured according to EN 12102 under standardized laboratory conditions and is the basis for comparison between different manufacturers and models. It indicates how much sound energy the source emits in total – regardless of where you are located.

The sound pressure level, on the other hand, is what you or your neighbors actually hear. It describes the perceived loudness at a specific location and decreases with distance from the sound source. A simple rule of thumb: Doubling the distance reduces the sound pressure level by about 6 dB(A).

Both values are given with A-weighting, i.e., in dB(A). This weighting filters the measurement signal according to human hearing sensitivity. Our hearing is particularly sensitive in the mid-frequency range between 1,000 and 4,000 Hz, while very low and very high frequencies are perceived less strongly.

The OCHSNER AIR HAWK 208 has been certified as the quietest air/water heat pump ever measured by OCHSNER at the Swiss Heat Pump Test Center in Buchs. The measurement values according to EN 12102 speak for themselves: The outdoor unit achieves a sound power level of 45 dB(A) and a sound pressure level of 28 dB(A) at a distance of 3 meters.

To put these numbers into perspective: 28 dB(A) at a distance of 3 meters is 2 dB below the Austrian guideline value of 30 dB(A) at the property boundary and already at a shorter distance, where the sound level is usually higher. Compared to the German nighttime immission guideline value of 35 dB(A) for pure residential areas, there is even a difference of 7 dB. This is at the acoustic level of whispering or very light wind.

The comparison with the competition makes the dimensions clear: Common air/water heat pumps achieve sound pressure levels between 35 and 42 dB(A) at a distance of 3 meters. The difference of 7 to 14 dB to the OCHSNER AIR HAWK 208 means, due to the logarithmic decibel scale, a 5 to 16 times lower subjectively perceived loudness. This is not a marginal difference, but a huge leap in sound quality.

The Whisper Management combines optimized air flow, vibration-damping mounting, and acoustically optimized housing geometry. The system does not simply work with a blanket speed reduction, but takes the outside temperature into account. On mild nights, when the heat demand is low anyway, the speed is reduced more than on very cold nights when full heating power is needed.

The fans operate fully modulating and continuously adjust their speed to the current heat demand. At partial load, which prevails during most of the heating period, the sound emissions decrease accordingly.

Even the quietest heat pump can become a nuisance if it is placed incorrectly. The installation location is not an afterthought, but a planning task that must be considered during the design phase.

Minimum distances to the property boundary are not only legally relevant but also acoustically sensible. For residential areas, we recommend at least 3 meters to the property boundary. Depending on the sound power level of the chosen model and the local conditions, a greater distance may be required. A professional sound prediction takes all these factors into account and determines the expected immission levels under real conditions.

Quiet begins with planning. The best heat pump is of little use if the installation location is acoustically poorly chosen. A certified OCHSNER system partner will advise you on optimal installation, create a sound prediction if necessary, and ensure that not only the heating performance but also the sound protection meets the highest standards.

The installation location is the decisive success factor. Sound-reflecting surfaces such as house walls, garage doors, or walls reflect sound and can lead to level increases of 3 to 6 dB. That may sound like little, but it corresponds to a doubling to quadrupling of the perceived loudness. Corners and niches are particularly problematic. Here, the sound level can increase by up to 10 dB due to overlap and reflection. A heat pump that achieves 28 dB(A) when freely placed can suddenly be at 38 dB(A) in a corner between two house walls, thus losing the entire advantage.

The sound direction also plays an important role. The air discharge side should not be directed directly towards protected rooms – neither towards your own bedrooms nor those of neighbors.

The foundation must be vibration-damping. Body sound transmissions through the building can otherwise become audible in the interior, even if the outdoor unit is correctly installed. A concrete foundation slab with an underlying vibration-damping layer has proven effective in practice.

For particularly sensitive areas, OCHSNER offers the Super Silent Package as an option. This package utilizes design optimizations derived from the aviation industry. Specifically, it consists of cylinder silencers that are attached to each fan. These achieve an additional sound reduction of 3 dB(A). That may sound like little, but due to the logarithmic scale, it is a significantly noticeable improvement.

With the optional Super Silent Package, we achieve approximately 25 dB(A) at a distance of 3 meters. This puts the heat pump below the Austrian requirement value for indoor spaces at night – measured in the outdoor area. This is a remarkable value that shows how advanced OCHSNER heat pump technology already is today.

The Super Silent Package is particularly recommended in densely built row house settlements or in direct proximity to bedrooms.