Heat pump noise: why our heat pumps are quiet

A major factor of any household appliance—particularly one that does such heavy lifting as heating the house or making hot water—is how loud it will be when operating. There is no point having a dreamy, relaxing, soothing home temperature, if the machines doing the work are blasting out uncomfortable and disturbing industrial noise.

Unfortunately, with the way many companies test and deliver these products, you can be left without any idea of how the unit will sound. Without a clear standard, you can end up with heating devices that compete with your TV (70dB) for acoustic attention.

At Stiebel Eltron we are known for producing particularly quiet heat pumps - both our air source and our ground source models are renonowned for their whisper-quiet operation. The reason for this is that we pay particular attention to testing and building our products to ensure low noise emissions.

Standards are Important

Imagine for a moment you’re not shopping for a world class heating system, but a new sound, a record to ease the trials of the day… you select a wonderful cello concerto, soft reedy notes that will let you drift into a wonderfully relaxing dreamland. You buy the record, remove the plastic sleeve and place the vinyl on the turntable.

You gently place the needle on the record… but something's wrong—distorted guitars and hard-hitting snares tear through your ears. Instead of strings you have distortion.

The record was labelled incorrectly, soothing cellos, is actually shredding amp-breakers, way louder than the guy at the shop said. It was his idea of a relaxing vinyl. But his idea—his testing—is different to yours.

Sound Power Level / Sound Pressure

Using Sound Power Level and Sound Pressure in the EN 12102 standard STIEBEL ELTRON gives you a truly comparable idea of how each unit will perform acoustically at home.

Sound Power Level

Sound Power Level is not an eighties hair metal band. It is the pure sound energy output (in Watts) at the boundary of the device, measured in dB(A) as it would be perceived by the human ear in an open space environment and in perfect lab testing conditions (the above-mentioned anechoic chamber). It’s a wonderful engineering metric that sets a solid cornerstone of acoustic comparison.

Sound Pressure

Sound Pressure is the effect of the Sound Power Level in the environment. It is the physical, measurable output of the sound perturbations from the device, in a specific orientation and place. Think of it as that potential sound coming out of the unit and received by your ear in the real world. This is the metric that really matters because it takes into consideration such determining factors like how sound is affected by air and the surroundings in the distance from the unit to your ear. What these metrics mean is that you can compare our units with sounds in the real world. There are no hair metal surprises when you flick the switch on installation.

Metrics in Action

A STIEBEL ELTRON WPL 25 air source heat pump has a Sound Power value of 54dB and Sound Pressure (at 5 metres distance in an open field) of 32 dB. The theoretical sound output is drastically reduced by movement of 5 metres in the open air—it’s not hard to imagine what modern insulation can do.

The encased compressor design of these models can be further muted by placement and orientation on installation. The friendly STIEBEL ELTRON team can assist you to bring the sound pressure down from the conversational or babbling brook 40-45dB, to rustling leaves 20 dB or a softly breathed whisper of 10 dB.

Sound Practice

Using the EN 12102 standard, there are no second guesses and you are never in the dark about how loud (or quiet) your unit will be. STIEBEL ELTRON uses the metrics of Sound Power Levels and Sound Pressure to give you the clearest idea possible about how quiet your STIEBEL ELTRON powered life will be.

Sound Checklist

To make sure you are comparing cellos with cellos and eighties hair metal with eighties hair metal use this checklist.
  • Is sound output measured in;
    –Sound Power (Watts)?
    –Sound Power Level (dB)? or
    –Sound Pressure (dB)? and at what distance?
  • What were the testing methods?
  • Are the figures theoretical or was the unit physically tested in an anechoic chamber?
  • Was the testing overseen by an accredited, independent third party?
  • Does the testing and comparison fall under a standard like the European Standard EN12102?
Ask these questions of your manufacturer,
know the song your unit is singing,
STIEBEL ELTRON has the answers for you.