Quietest heat pumps UK compared: published dB figures and what they mean

Quick answer: Worcester Bosch’s Compress 5800i AW is the quietest heat pump on published figures, at 40 dB(A) sound power for the 4kW. Grant’s Aerona 290 4kW follows at 48.0 dB(A), then LG’s Therma V and NIBE’s S2125 at 49 dB(A). The loudest mainstream unit we found is Samsung’s 16kW at 65 dB(A).

We haven’t tested these units or measured anything ourselves. Every figure below is the manufacturer’s own published sound power level to EN 12102, taken from datasheets and installation manuals, checked on 28 July 2026.

Sound power and sound pressure are not the same thing

This trips up nearly everyone, including some retailers. Sound power is the total acoustic energy the unit emits, a property of the machine, quoted in dB(A) and measured to EN 12102. Sound pressure is what you’d hear at a stated distance, and it falls as you move away.

A unit with 55 dB(A) sound power might show 41 dB(A) at 1 metre and 34 dB(A) at 3 metres. All three numbers are correct and only one of them describes the machine. When a listing says 35 dB(A) with no distance attached, it’s a sound pressure figure being passed off as a specification. Ask which it is.

Published sound power, quietest first

Two figures worth arguing about

Worcester’s 40 dB(A) is the outlier. It’s eight decibels below anything from another brand, and roughly a quarter of the perceived loudness of a Daikin Altherma 3 M 8kW. Worcester publishes it in its own specifier guide, to EN 12102. So it stands until somebody measures otherwise. And if it holds up in the field, it changes where a heat pump can go on a terraced street. That’s a big if.

LG’s is the opposite problem. LG publishes a rated sound power of 49 dB(A) for the 7, 9 and 12kW. Its 7 and 9kW datasheet also carries a daytime maximum, 58 and 60 dB(A), measured at maximum fan and compressor speed with 2°C outside. Both are honest. Only one of them gets reproduced by retailers. If your installer runs the planning calculation on the rated figure and the unit sits at daytime max on a cold January morning, the sums were done on the wrong number.

Vaillant is worth a mention too. Its own manual gives 51 to 53 dB(A) sound power, but several UK trade listings advertise the aroTHERM plus at 44 dB(A) on the strength of its Quiet Mark accreditation. That figure doesn’t appear anywhere in Vaillant’s EN 12102 table.

What the planning rules actually require

Since 29 May 2025, air source heat pump installations in England have had to comply with MCS 020(a) to qualify for permitted development. Your installer runs the MCS sound calculator. It takes the unit’s sound power level, the distance and the reflective surfaces around it, and has to show 37 dB(A) or less at 1 metre from the nearest neighbouring habitable room window or door. MCS 020(a) replaced the old MCS 020 calculation, which used a 42 dB(A) figure that included background noise.

Three other things changed at the same time. The old rule requiring at least 1 metre from the property boundary was removed. The maximum unit volume for a house went up from 0.6 to 1.5 cubic metres. And up to two units are now allowed on a detached home. Since 29 May 2026, when the transition ended, MCS 020(a) is the only route: the previous ‘equivalent’ acoustic method is closed.

The practical effect is that a quiet unit buys you siting freedom rather than a quieter garden. Our heat pump noise and planning guide goes through the calculation, and what heat pumps sound like on terraced streets covers real-world siting.

What actually makes a heat pump noisy in practice

Position beats specification. A quiet unit in an enclosed side passage with two hard walls reflecting sound will measure worse than a louder one in an open garden. Mounting matters too: anti-vibration feet on a solid slab, not bolted to a hollow wall that becomes a soundboard.

Oversizing is the other cause. A machine too big for the house runs at high fan speed in short bursts instead of ticking over, and the on-off cycling is what neighbours notice. Correct sizing is a noise measure as much as an efficiency one. See our sizing guide.

If noise is your deciding factor

Shortlist the Worcester Bosch CS5800i AW first, then the Grant Aerona 290 4kW and the NIBE S2125. Anything above 55 dB(A) sound power isn’t a noise-constrained buy, whatever the brochure says about quiet mode. Ask your installer for the MCS sound calculator output for your specific position before you sign anything, and ask which sound power figure went into it. Then compare on everything else in our brand comparison or check budget with the calculator.

FAQs

How loud is 40 dB(A) in real terms?

Sound power of 40 dB(A) works out at roughly 32 dB(A) sound pressure at 1 metre, which is quieter than a domestic fridge. At 3 metres you would struggle to hear it over background traffic. A 60 dB(A) sound power unit is closer to a conversation held next to you.

Do I need planning permission if my heat pump is over 37 dB(A)?

The 37 dB(A) test is measured at the neighbouring window, not at the unit, so a 55 dB(A) sound power machine can still pass with the right siting. If the calculation fails, you need a planning application rather than permitted development. Scotland, Wales and Northern Ireland have their own rules.

Does quiet mode cost efficiency?

Yes. Vaillant’s manual shows the aroTHERM plus dropping from 51 to 46 dB(A) sound power at 60% noise reduction, with heat output at -7°C falling from 3.6kW to 2.2kW on the 3.5kW unit. Quiet mode is useful overnight, not as a permanent setting.