Make your PortaSplit quieter: damping casing rattle

To apply the mat you have to open the casing. This usually voids the manufacturer's warranty, and you do it at your own risk. Unplug the unit first, do not touch anything on the refrigerant circuit and only go ahead if you are confident.

You need a self-adhesive butyl-aluminium damping mat (about 2 mm thick), a utility knife, a pressure roller or a solid object, and some foam for the areas around the fan.

Our own photos of the modification on our PortaSplit – the pictures show which panels are worth treating.

Any self-adhesive butyl-aluminium mat from the car accessories sector (door damping), about 2 mm thick, will do. A 0.5 m² roll is enough for the indoor unit. The mat can be cut with a utility knife and sticks to clean plastic straight away. We used a mat from HASKYY; comparable products are available from any car accessories retailer.

Unlike a permanently installed split system, the PortaSplit has its compressor in the indoor unit – outside, only the condenser and its fan are at work. The compressor produces a low-frequency hum that is strongest at start-up and varies with load during operation. This basic noise cannot be damped away, only reduced by lowering the load (silent mode, higher target temperature).

What most people find annoying, however, is not the hum itself but the casing resonating along with it: thin plastic panels that rattle, clatter or buzz in time with the compressor. This is exactly where butyl damping helps – it makes the panels heavier and stiffer so they no longer resonate. On top of that come vibrations transmitted through the castors to laminate or floorboards, and occasionally a clicking from the valve when switching between cooling and heating.

Before you reach for the screwdriver, try these steps – they cost you nothing in terms of warranty:

The outdoor unit itself is quiet, but it transmits vibrations to whatever it stands on. A sheet-metal windowsill or a thin balcony railing then acts as a sounding board – and the neighbours hear more than you do. Put the unit on rubber buffers or a rubber mat, do not hang it on thin sheet metal and make sure the condensate hose does not knock against the façade. The “Quieter outdoor unit” mode also lowers the outdoor fan speed, which makes the biggest difference at night.

Sticking foam around the outside of the casing impairs cooling and hardly dampens anything – the sound comes from the vents, not through the walls. A blanket over the unit is a fire risk. Putting the unit in a cupboard or behind furniture chokes the air supply and makes the compressor work harder, which makes it louder. And having refrigerant “topped up” because the unit hums is a waste of money – the hum is down to the design, not a fault.

You don't need a full toolbox for the job: a Phillips screwdriver for the casing screws, a plastic spudger or an old loyalty card to release the clips, a utility knife, a ruler, a lint-free cloth with a little isopropyl alcohol for degreasing and a small pressure roller (a wallpaper seam roller works too). Plus 0.5 m² of 2 mm butyl mat and a piece of self-adhesive foam for the areas close to the fan. Time needed: about an hour, if you photograph the screw positions with your phone.

On our unit the result was clear: the metallic clatter when the compressor starts up is gone, and so is the buzzing of the side panels. What remains is the deep hum of the compressor – but steady and without extra noises, which subjectively is far less disturbing than a quieter but rattling unit. Since then, the PortaSplit has been running in the bedroom in silent mode at a target temperature of 25 °C, and nobody wakes up any more when the compressor starts.

We measured with a smartphone app at a distance of one metre: before, around 47 dB in normal operation with clear peaks at start-up; afterwards, around 44 dB with no peaks. That is not a lab value, but it shows the trend. Important: after reassembly, check all vents – butyl mat or foam must not narrow the airflow anywhere, otherwise cooling capacity drops and the compressor works harder.

By the way, the same principle works on any monoblock with a thin plastic casing – Comfee, Klarstein and Suntec benefit just as much. On De'Longhi units with thicker casing walls the effect is smaller; there, decoupled placement is the better investment.