When a heatwave settles over Germany, a mobile air conditioner is the fastest way to make one room genuinely comfortable without drilling holes or calling an installer. But the category is full of confusing labels — monoblock, split, BTU, energy class — and the good units vanish from shelves within hours. This guide explains exactly what to look for, how to size and set one up, and how to actually find one in stock.
What is a mobile air conditioner?
A mobile air conditioner is a portable, plug-in unit that refrigerates the air in a single room and pumps the heat it removes outside through an exhaust hose. Unlike a fan, which only moves air, an AC actually lowers the room's temperature — but only if the hose vents the hot air outdoors and the room is reasonably sealed. That exhaust-hose requirement is the single most important thing to understand before buying.
Monoblock vs split: which type should you buy?
The two main types trade off price against noise and efficiency:
- Monoblock (single-hose): Everything sits in one box with one exhaust hose. Cheapest, simplest, and easiest to move room to room — but louder and slightly less efficient, because the unit draws in some room air it then has to replace.
- Split-style portable (like the Midea PortaSplit): Separates the compressor so the part in your room runs quieter, and it's typically more efficient. Pricier and the first to sell out, but the best experience if you'll run it in a bedroom or office for hours.
If quiet operation matters — a bedroom or a room you work in all day — lean split. If budget and simplicity win, a monoblock is perfectly good. Compare current options on the mobile air conditioner page.
How to size a mobile AC (BTU)
Cooling power is measured in BTU, and matching it to your room is what determines whether the unit actually keeps up. An undersized unit runs constantly and never reaches a comfortable temperature; an oversized one short-cycles and wastes energy. As a rough guide, larger and sunnier rooms, top-floor flats, and rooms with lots of glass need more BTU per square metre. Account for west-facing windows, kitchen heat, and the number of people in the room when you choose.
Running costs and energy class
A mobile AC uses far more electricity than a fan, so the energy label (A–G) matters for your bill if you'll run it daily. A more efficient class costs more upfront but less to run across a hot summer. To keep costs down: cool only the room you're in, keep doors and windows closed while it runs, shade the windows so the unit isn't fighting direct sun, and use a timer so it isn't cooling an empty room.
Noise: what to expect
Every mobile AC makes noise because the compressor and fan run continuously. Monoblocks are generally louder; split-style units are quieter in the room. If you're sensitive to sound at night, prioritise a model known for low decibels and a "sleep" or "night" mode that throttles the fan. Reading the rated noise level before buying saves a lot of regret.
Installing one in a rented flat
Most renters can use a mobile AC without any permanent changes:
- Vent the hose through a window or door. A window-sealing kit (a fabric or panel insert) closes the gap so hot air doesn't leak back in.
- Don't drill if you don't have to. No-drill sealing kits keep you within tenancy rules and are easy to remove when you move.
- Drain or self-evaporate. Some units collect condensate you empty; many self-evaporate most of it through the hose.
- Mind the cable and tilt. Keep the unit upright and on a level surface, and let it settle before first use after transport.
For the cooling to work, the room has to be sealed — an open window with an unsealed hose lets the heat you're pumping out flow straight back in.
Where to buy a mobile AC in stock
The hardest part in a heatwave isn't choosing a model — it's finding one that's actually in stock near you. Rather than driving to stores that sold out yesterday, check a live availability map by postal code, sort by distance, and reserve for pickup. If everything nearby is red, set a back-in-stock alert so you're notified the moment a store restocks. That's the whole point of this site: see which mobile ACs are in stock near you before you leave the house.
The bottom line
A mobile air conditioner is the most effective portable way to cool a German flat in a heatwave. Pick monoblock for price or split for quiet efficiency, size it to your room, seal the window the hose vents through, and — most importantly — buy before the heat peaks or set an alert, because the good units don't stay on shelves long.