Monoblock vs. Fixed Split vs. Mobile Split: Which AC Actually Fits a Renter?

The three ways to cool a rented flat work very differently, and only some of them are yours to install without asking. Here's how each one works, what it costs you in comfort and effort, and which type a renter in Germany can actually use.

6 min read · Updated July 2026

When you start shopping for an air conditioner as a renter, you quickly run into three words that get used almost interchangeably: monoblock, split, and mobile split. They are not the same thing, and the difference matters far more than the price tag. One type you can plug in and forget. Another needs a certified technician, a hole in the facade, and your landlord's signature. This guide walks through how each one actually works, what you trade off, and which type a renter in Germany can realistically use.

Monoblock: one box, one exhaust hose

A monoblock is the classic portable air conditioner. Everything (compressor, condenser, evaporator) sits inside a single unit on wheels. It cools the room and pushes the waste heat outside through a flexible exhaust hose that you feed through a tilted window or a door gap with a seal kit.

Because it is fully self-contained, there is nothing to install and nothing to connect. You roll it in, run the hose to the window, and switch it on. That simplicity is why it suits rented flats: there's nothing to drill, no refrigerant work, and the device itself needs no permission.

• Pros: no installation, no permit for the device, movable between rooms, low upfront cost, you take it with you when you move.
• Cons: louder because the compressor is in the room with you, less energy-efficient than a split, and the open window gap around the hose lets some warm air leak back in.
• Best for: renters who want a cool bedroom on hot nights without touching the building at all.

Mobile split: quieter, with a small outdoor unit

A mobile split (sometimes called a portable split) separates the noisy part from the cold part. The compressor sits in a small outdoor unit, whether on the balcony, a windowsill bracket, or the floor outside, while the indoor unit blows cold air into the room. The two halves are joined by a thin, pre-filled refrigerant line.

The important detail for renters is the sealed, factory-charged type. Here the refrigerant circuit is closed and hermetically sealed at the factory with quick connectors, so no one has to open the refrigerant system on site. That keeps it in the same permission-free category as a monoblock while giving you noticeably quieter operation and better efficiency, since the compressor's noise and heat stay outside.

• Pros: much quieter indoors, more efficient than a monoblock, still needs no facade penetration and no certified refrigerant work when the circuit is sealed and pre-filled.
• Cons: you need somewhere to place the outdoor part (balcony or window), and it is a bit more effort to set up than rolling in a single box.
• Best for: renters with a balcony or accessible window who want split-level comfort without a permanent installation.

Fixed split system: the powerful one you probably can't install

A fixed split system is what most people picture as "real" air conditioning: a permanent indoor unit on the wall, a compressor unit mounted outside on the facade, and copper refrigerant lines running through a drilled hole between them. It is the quietest and most efficient option by a wide margin, and it can heat as well as cool.

The catch is everything that makes it fixed. The refrigerant lines have to be connected and charged on site, which under the EU F-Gas Regulation may only be done by a certified firm with the proper qualification (Sachkundenachweis). It requires drilling through the exterior wall and bolting a unit to the facade, which changes the substance of the building. For a renter that means written landlord consent, and in a condominium it often needs the owners' association (WEG) to approve it too.

• Pros: quietest, most efficient, cools and heats, permanently out of the way.
• Cons: needs a certified installer, permanent facade work, landlord (and often WEG) approval, high cost, and you can't take it with you.
• Best for: owners, or renters with an explicit long-term agreement and a landlord who wants the upgrade. It is not a plug-and-play renter solution.

What a renter in Germany actually needs to know

The legal line runs between the device being self-contained and the building being altered. Monoblocks and sealed mobile splits are permission-free because you are not touching the structure and not opening a refrigerant circuit. A fixed split is permit-territory because you are drilling the facade and doing on-site refrigerant work that is regulated.

• No structural change: you still may not drill through the facade, mount brackets permanently, or damage the property, even with a permission-free device. Route the hose through a window and use a proper seal instead.
• F-Gas rule of thumb: if a technician has to open and charge the refrigerant system on site, it needs a certified firm. Factory-sealed, pre-filled units avoid this entirely.
• Landlord consent: you don't need it for the appliance itself, but you do need it for anything permanent attached to the building. When in doubt, a short written note to your landlord keeps you on the safe side.
• Moving out: permission-free units go with you; a fixed split stays and has to be paid for and maintained accordingly.

So which type fits you?

If you just want a cooler bedroom and zero hassle, a monoblock is the honest answer. If you have a balcony or an accessible window and quiet nights matter to you, a sealed mobile split gives you a real step up in comfort while staying permission-free. A fixed split is genuinely the best machine, but it belongs to owners and long-term arrangements, not to a renter who wants to be cool this summer without a building project.

If the idea of buying, storing, and reselling a unit is the part that puts you off, seasonal rental of a permission-free device is worth a look. You get the cooling for the summer and hand it back when the heat is over. Whichever route you take, the rule is simple: keep the device self-contained, leave the building untouched, and you stay firmly on the right side of the line.

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