How to read HVAC noise ratings for a quiet office
The dB(A) figures on data sheets are hard to compare because makers mix sound power and sound pressure. This guide explains both values, gives concrete limits for offices and measurement rooms, and shows how to compare air conditioners and fans fairly.
View quiet air conditionersSound power or sound pressure - what is on the sheet?
Data sheets show two very different dB(A) values: the sound power level LWA and the sound pressure level LpA. Sound power describes the total acoustic energy the unit radiates and is a property of the device, independent of the room. Sound pressure is what the ear actually hears at a given distance.
The difference is large: sound power and sound pressure at a typical distance usually differ by 9 to 11 dB. A unit rated 54 dB(A) sound power corresponds to roughly 44 dB(A) sound pressure at 1 m - both numbers describe the same device.
- LWA (sound power): a device property, independent of distance and room, measured to EN ISO 3744.
- LpA (sound pressure): depends on distance, room acoustics and installation, always quoted with a distance (e.g. at 1 m).
- Rule of thumb: in free field LWA is about 9 to 11 dB higher than LpA at 1 m.
How do you compare dB(A) ratings fairly?
The decibel scale is logarithmic, so the raw number is misleading. A rise of 10 dB is perceived as roughly twice as loud, while just 3 dB already means double the acoustic energy and is barely audible in daily use. Small numeric gaps matter more than they appear.
Also check the test condition. Air conditioners are often advertised at the quietest fan step but run higher in service. Compare the value at medium or maximum speed and check whether the outdoor unit of a split system is stated separately.
- Always check the fan step and distance of the rating, not just the bare number.
- For split units, judge indoor and outdoor sections separately.
- Mind the frequency content: low-frequency hum disturbs an office more than the plain dB(A) value suggests.
What limits apply to offices and measurement rooms?
For mental work in offices, VDI 2058 and the German workplace rule ASR A3.7 set a rating level of no more than 55 dB(A) for predominantly mental tasks, with up to 70 dB(A) for simple office work. As a comfort target for focused work, however, 35 to 45 dB(A) has become the accepted range.
In a measurement or calibration room, constancy matters as much as the raw level. A steady soft hiss disturbs less than cyclic on-off switching, which can affect sensitive balances and instruments through vibration. Inverter-controlled air conditioners modulate continuously and therefore stay quieter and steadier.
Frequently asked questions
Why are there two different dB values on the data sheet?
The higher figure is usually the sound power L(WA), the lower one the sound pressure L(pA) at a stated distance. Both describe the same unit but are not directly comparable. Only compare like with like.
How many dB(A) is acceptable for an office?
For focused work, 35 to 45 dB(A) sound pressure at the workplace is considered comfortable. ASR A3.7 allows up to 55 dB(A) rating level for mental work, but that is the upper limit, not a comfort value.
Is a unit 3 dB quieter really quieter?
Yes. 3 dB is half the sound power and is audible in daily use. Only about 10 dB difference is perceived as half as loud, yet even small dB gaps can decide a purchase.
What matters more than raw dB(A) in a measurement room?
Constancy and frequency content. Steady noise disturbs less than cyclic on-off switching, and low-frequency hum can affect sensitive instruments through vibration. Inverter units run more smoothly.
Looking for a quiet unit for an office or measurement room?
We advise on correct sizing by sound power and supply inverter-controlled, low-vibration units with honest dB(A) ratings.
Honest ratings
Sound power to EN ISO 3744, clearly separated from sound pressure.
Standard-compliant
Sizing to VDI 2058 and ASR A3.7 for workspaces.
Quiet technology
Inverter units modulate continuously and stay steady.
Expert advice
Our specialists size units to your noise limit.