Air conditioning in a rented flat: what is allowed – and what isn't

A portable air conditioner – monoblock or mobile split – is a household appliance. It plugs into a socket, the hose goes through the tilted window, and nothing is drilled or permanently altered. You need no permission for it, any more than for a tumble dryer. When you move out, you simply take it with you.

A fabric window seal or a fitted sealing panel can also be removed without leaving a trace and is therefore unproblematic. It is a different story if you want to drill a hole through the wall – that is a structural alteration.

Core drilling through the outer wall, an outdoor unit on the façade, refrigerant lines: that is a structural alteration for which you need your landlord's written consent. They may refuse it or attach conditions, such as removal when you move out or installation by a specialist firm. In owner-occupied flats, the owners' association (WEG) must also agree, because the façade is common property.

The outdoor unit of a mobile split on the balcony or windowsill is not an intervention in the building – as long as nothing is screwed on. Check the house rules for any conditions regarding balconies. Consideration for your neighbours is what matters: noise limits are considerably stricter at night than during the day (in residential areas roughly 35–40 dB(A) outside the neighbour's window). Use night mode, don't place the unit directly below other people's bedroom windows and decouple the outdoor unit so no vibrations travel through the railing.

Condensate must not drip onto the neighbours' balcony or the pavement. With a mobile split, lead the condensate into a container or through a hose into a drain; with a monoblock, empty the tank in good time. Dripping water on the neighbour's balcony is the most common trigger for disputes – not the noise.

If you live in a flat you own, you are just as free as a tenant when it comes to a portable unit. It is different for anything that touches the façade, the roof or load-bearing walls: the outer wall and façade are common property, and a core-drilled hole or a permanently mounted outdoor unit is a structural alteration that the owners' meeting has to vote on. Since the German condominium law reform (WEG reform), a simple majority is enough, and the costs are usually borne by whoever wants the alteration. Without a resolution, you risk having to remove it – even years later.

If your landlord agrees to a permanent system, they may set conditions: installation by a specialist firm, proof of liability insurance, removal at your expense when you move out, no disturbance to neighbours, and possibly a deposit for the removal. What they may not demand is that you remove a portable unit that leaves no marks and respects quiet hours. Get every consent in writing – verbal promises are worthless if the property changes hands.

If you do want a permanent system, a factual request helps: describe the unit (manufacturer, model, sound power level), the planned location of the outdoor unit and the specialist firm doing the installation, and offer to remove it when you move out or to hand the system over for a transfer fee. Enclose the spec sheet and a sketch. Many landlords agree once they see that you have thought about noise, appearance and removal – after all, air conditioning also increases the value of the flat.

Before you cool, keep the heat out: external shutters or blinds are the most effective heat protection, but they are a structural alteration. Allowed without asking are heat-protection films fitted inside the windows (removable without residue), thermal curtains, shade sails on the balcony and cross-ventilation at night. Combined with a portable air conditioner, a smaller model is often enough – one that runs more quietly and uses less electricity.

In short, here is what to keep in mind as a tenant or flat owner:

If a neighbour complains, what counts is not your perception but the measured value outside their open window. The benchmark in Germany is the guideline values of the TA Lärm (Technical Instructions on Noise Protection): in general residential areas 55 dB(A) during the day and 40 dB(A) at night; in purely residential areas 50 and 35 dB(A). The outdoor unit of a mobile split is usually 50–55 dB(A) at a distance of one metre, and around 15 dB less at five metres – uncritical during the day, borderline at night depending on distance. Night mode, decoupled placement and a location away from the neighbour's window resolve almost every dispute before it starts. A conversation in advance often achieves more than any measurement.

You simply take portable units with you; adhesive residue from a window seal comes off with a little methylated spirit. With a permanently installed system, your landlord's consent governs what happens when you move out: removal at your expense, including sealing the core-drilled hole – or takeover by the next tenant for a transfer fee, if the landlord agrees. Clarify this before installation, not at the handover of the flat.

Document the condition of the window, windowsill and balcony with photos before setting up for the first time. Scratches from the outdoor unit or marks from the hook-and-loop tape of the seal are rare, but if there is a dispute about the deposit when you move out, dated pictures are the only argument that counts.