Cool Your Berlin Apartment Legally, Without Renovation or Landlord Fights

Some air conditioners need a landlord's signature and a certified installer. A whole category needs neither. Here's where the legal line actually runs for renters.

6 min read · Updated July 2026

Berlin summers get hot, and most old apartments were never built to cope with it. Still, plenty of renters assume that any air conditioning means a fight with the landlord, an expensive installer, and holes in the wall. It doesn't have to. There's a whole category of cooling devices you're allowed to set up on your own, with no permit and without drilling a single hole.

What "cooling legally" actually means

In German tenancy law, the line that matters is whether you make a structural change to the flat (bauliche Veränderung) or damage its substance (Substanzverletzung). Anything you can put in the room, use, and take out again without altering the building is yours to decide as the tenant. The moment you drill into a wall or the facade, run refrigerant lines through the masonry, or mount an outdoor unit, you're changing the building, and that needs your landlord's consent.

The devices you can use without permission

• Portable monoblock units (single- or dual-hose): the whole machine sits in the room, and warm air leaves through an exhaust hose fed out of a tilted window. You plug it in and switch it on.
• Window air conditioners: fitted into the window frame itself, with no opening cut into the wall.
• Permanently sealed mobile split units (monoblock splits): they have an indoor and an outdoor part, but the refrigerant circuit is hermetically sealed at the factory and the line passes through a window feed-through, with no work on the wall.

What they share: no drilling into walls or the facade, fully removable, and nobody ever opens the refrigerant circuit. That's why you need neither a landlord permit nor a certified refrigeration firm to run them. Setup really just means positioning the unit and sealing the window. If you'd rather not deal with the exhaust kit yourself, a service like KlimaLegal offers optional setup, but you're legally free to do it alone.

When you do have to ask your landlord

Classic fixed split systems are a different story. They have an outdoor condenser mounted on the facade or balcony, and refrigerant lines routed through the wall. That's a structural change, so you need written consent from your landlord before anyone starts. In practice it usually also means a certified installer, and in a building with multiple owners it can require approval from the owners' association. Many older Berlin buildings sit under heritage protection (Denkmalschutz), which limits what you can attach to the facade. Even a bracket screwed into the outside wall counts as a change. If you rent, get the yes in writing before the work begins.

F-Gas and refrigerant, briefly

EU F-Gas rules govern who is allowed to open and fill a refrigerant circuit. A fixed split system has to be installed by a certified refrigeration technician with the required qualification (Sachkundenachweis, sometimes called the Kälteschein). Portable monoblocks and sealed mobile splits arrive pre-charged and closed, many of them running on the natural refrigerant R290 (propane), so you as the tenant can set them up yourself. You never touch the circuit, which is exactly why no certificate is required on your end.

Practical tips for Berlin flats

• Seal the window: use a proper window feed-through or sealing kit so the warm air the unit pushes out doesn't leak straight back in. This matters most with the tilt-and-turn windows common in Altbau.
• Condensate: monoblocks produce water. Many self-evaporate most of it, but plan for a tank or a drain hose on humid days.
• Noise and house rules: keep the fan noise in mind for neighbours and respect quiet hours (Ruhezeiten), especially at night.
• Power draw: portable units are less efficient than fixed splits. Check the EER rating, cool one room with the doors closed, and run it in the evening when it's cheaper and cooler.
• Removability: keep everything reversible so you can hand the flat back exactly as you got it.

The short version: you don't need a renovation, a permit, or an awkward conversation with your landlord to get through a Berlin heatwave. Pick a portable monoblock, a window unit, or a sealed mobile split, seal the window properly, and you're cooling your flat within the rules. Save the landlord request for a fixed split system, the one case where the building itself changes.

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