Two decibel figures for one machine: power against pressure
Samsung publishes 41 dBA and 55 dBA for the same heat pump. Which figure a data sheet is giving you, and why comparing across the two reverses the answer.
What this means
Sound power is the acoustic output of the machine and does not depend on where you stand. Sound pressure is what a microphone reads at a stated distance. Samsung publishes both for the EHS Mono R290, at 41 dBA pressure and 55 dBA power, so a figure quoted without saying which it is can be wrong by fourteen decibels.
Equipment and model context
Cross-brand explanation; product figures come from the model documentation
- Samsung EHS Mono R290
- Worcester Bosch Compress 5800i AW and Grant Aerona 290
- Vaillant aroTHERM plus, NIBE S2125, and Carrier residential heat pumps
The figures quoted are manufacturer-published laboratory values under the standards each names, most often EN 12102 for sound power. None of them predicts what a neighbour hears, which depends on distance, mounting, reflecting surfaces, and background level.
What this guide covers
- Two heat pump quotations with decibel figures that do not seem comparable.
- A planning or permitted development condition written against a noise limit.
- A brochure figure that does not match what the unit sounds like on site.
What changes the answer
- Manufacturers publish sound power, sound pressure, or both, and label them briefly.
- The two quantities differ by an amount that depends on distance and surroundings.
| Published figure | Quantity |
|---|---|
| Samsung EHS Mono R290, 41 dBA | Sound pressure |
| Samsung EHS Mono R290, 55 dBA | Sound power, same machine |
| Worcester Bosch Compress 5800i AW, 32 to 34 dB(A) | Sound pressure at one metre |
| Worcester Bosch Compress 5800i AW, 40 to 42 dBA | Sound power |
| Grant Aerona 290, 37.0 to 42.6 dB(A) | Sound pressure at one metre |
| NIBE S2125, 49 dB(A) LWA | Sound power under EN 12102 |
The two quantities, and why one is always larger
Sound power is a property of the source. It is the total acoustic energy the machine emits per second, and it stays the same figure whether the unit sits in a field or a courtyard. It cannot be measured directly with a meter held up to the unit; it is derived from measurements under a defined standard, which is why data sheets cite EN 12102 beside it.
Sound pressure is what a meter reads at a point. It falls with distance from the source and rises when hard surfaces reflect energy back, which is why a figure is only meaningful with the distance attached, as in Worcester Bosch's 32 dB(A) at one metre.
Sound power is the larger number for any given machine, and the gap between the two is not a fixed offset. Samsung's pair, 41 dBA pressure and 55 dBA power, is fourteen decibels apart on one unit.
Reading which figure a data sheet is giving
Three signals identify it. The letters LWA denote sound power, as on NIBE's S2125 sheet giving 49 dB(A) under EN 12102 at a 7 by 45 condition. A stated distance means sound pressure, as with Grant's 37.0 to 42.6 dB(A) at one metre across the Aerona 290 range. A named operating condition means the figure is one point on a curve rather than a single property.
That third signal matters more than it looks. Vaillant publishes aroTHERM plus sound power at A7/W35, A7/W45, and A7/W55, and the readings climb: 51, 53, and 54 dB(A) on the 3.5 and 5 kilowatt units. A single quoted figure for that unit is one of three.
Where a manufacturer publishes only one number and does not say which quantity it is, the comparison to a competitor is not available. It can still be compared inside that manufacturer's own range, where the convention is at least consistent.
What the number does not tell you
None of these figures describes what will be audible at a bedroom window. Distance reduces the pressure, a wall behind the unit reflects energy forward, a hard courtyard adds more, and the background sound level of the site decides whether what is left is noticed at all.
The tonal character of the sound is absent too. A compressor at a steady speed and a defrost cycle ending in a reversing valve are different experiences at the same measured level, and no single figure separates them.
Manufacturers publish what can be measured repeatably in a laboratory. Predicting a boundary level from it is an acoustic calculation using distance, directivity, and the surfaces on the site, which is what an assessment for a planning condition consists of.
Where the difference reaches a real decision
In the United Kingdom, siting an air source heat pump close to a boundary can bring a noise condition with it, and the assessment behind that condition starts from a sound power figure rather than a brochure decibel. Supplying the wrong quantity produces an assessment that is wrong in a known direction.
Within a range, the numbers do separate models usefully as long as the quantity is held constant. Vaillant's step from the 7 kilowatt unit to the 10 kilowatt is five decibels of sound power at A7/W35, and both figures are power, so the comparison holds.
Across manufacturers it is worth doing the work once: find the quantity, find the condition, find the distance if there is one, and only then compare. Two machines can differ by less than the difference between how their makers chose to describe them.
| What the sheet says | What it means |
|---|---|
| LWA, or sound power level | Sound power, independent of distance |
| A distance, such as at one metre | Sound pressure at that distance |
| EN 12102 cited | A sound power measurement standard |
| A condition such as A7/W35 | One point on a curve, not the whole product |
| Two figures for one unit | Almost certainly power and pressure together |
| A single unlabelled figure | Comparable inside that range, not across brands |
Only the first step belongs to the manufacturer. The other three belong to the site, which is why no published decibel figure can answer a boundary question on its own.
- Sound power of the unitMeasured under a standard, distance independent
- Distance to the receiverPressure falls as the sound spreads out
- Reflecting surfacesWalls, corners, and hard ground add energy back
- Background levelDecides whether the remainder is noticed
Questions people ask about this
What is the difference between sound power and sound pressure?
Sound power is the acoustic output of the machine and does not change with where you stand. Sound pressure is what a meter reads at a stated distance and falls as you move away. Samsung publishes 55 dBA power and 41 dBA pressure for the same EHS Mono R290 unit.
Which figure is on my heat pump data sheet?
Look for three signals. LWA or the words sound power level mean power. A stated distance, such as at one metre, means pressure. A citation of EN 12102 accompanies a sound power measurement.
Why is the sound power number always higher?
It describes the total energy leaving the source rather than the fraction arriving at one point, so it is larger for any machine. The gap is not a fixed offset: on the Samsung unit it is fourteen decibels, and it depends on the measurement arrangement.
Does the sound figure change with how the system runs?
It can. Vaillant publishes aroTHERM plus sound power at three water temperatures and the readings rise across them, from 51 to 54 dB(A) on the two smallest units. A system designed to run at a higher flow temperature sits at the higher figure.
Can I predict what my neighbour will hear from these numbers?
Not directly. Distance, mounting, reflecting surfaces, and background level all sit between a published figure and a boundary level, and an assessment for a planning condition is the calculation that connects them.
Evidence recordHow this page was checked
official manufacturer support article · checked 2026-09-07
Every technical claim above was written from primary documentation held in the HVAC Bench evidence record: Samsung Climate Solutions, Worcester Bosch, Grant UK, NIBE, Vaillant and Carrier technical literature. Where a source limits a definition to certain models, test conditions, or product classes, that limit is repeated here rather than generalised.
- Documentation class
- official manufacturer support article
- Scope of the definition
- Confirm against the exact model manual
- Last checked
- 2026-09-07