Quiet air conditioners compared

Manufacturers usually state either the sound power level or the sound pressure at one metre – which is not the same thing, and just 3 dB more already means double the sound energy. As a rough guide: 40 dB is a quiet library, 50 dB a quiet conversation, 60 dB a conversation at normal volume.

Monoblocks typically run at 52–65 dB because the compressor and condenser fan work inside the room. Mobile split units release the waste heat outside; the Midea PortaSplit reaches about 39 dB indoors in silent mode – but its compressor sits in the indoor unit, so it is much louder at full load.

Quietest of all are permanently installed split systems, where only a fan runs indoors (20–35 dB). Next comes the mobile split, then monoblocks with a dedicated silent mode (De'Longhi Pinguino Silent, Comfee Breezy Cool Pro, Trotec models labelled “Silent”) and finally basic monoblocks without night mode.

Many noises come not from the compressor but from the thin plastic casing resonating along with it. A firm, level footing and a decoupling mat help straight away. If you want to go further, you can line the casing from the inside with self-adhesive butyl-aluminium damping mat – our guide “Make your PortaSplit quieter” shows how to do this step by step on the PortaSplit (note: opening the unit voids the warranty).