🗓 Updated July 22, 2026 · EcoBack editorial team
Not every room needs an air conditioner. Whether a fan is enough or you need to actively cool depends mostly on four things: floor level, window direction, window area and insulation. The Heat Check weighs them and tells you what actually helps — in the right order.
The one number every purchase hangs on — it is already worked out below. Adjust the room size if it is off.
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Every portable unit here: no drilling, no installer, usually no landlord permission — hose to the window, seal around it, running in about 10 minutes, and it moves out with you. The one condition: without a sealed window every portable AC loses most of its effect — hot air gets pulled straight back in. Compiled from public tests & customer reviews — not tested by us. Prices vary; check the current price on Amazon. Illustrations, not product photos. Amazon.de ships to most EU countries, with site and checkout available in English.
De'Longhi Pinguino PAC EX105
Strong cooling, often in the test-winner line.
✓ Strong cooling, good efficiency
✕ Big & heavy
Comfee MPPH-09CRN7
Affordable for small bedrooms & offices — but clearly audible.
✓ Cheap, compact
✕ Clearly audible (~63 dB)
AEG ChillFlex Pro
Comfortable in the bedroom, well equipped.
✓ Very quiet, well equipped
✕ Higher price
De'Longhi PAC N90 ECO Silent
Monoblock test winner at Stiftung Warentest, silent mode, R290 refrigerant.
✓ Quietest monoblock in its group
✕ Pricier than the value pick
Klarstein Kraftwerk Smart 12K
Strongest cooling of its group in public comparisons.
✓ Strongest cooling of its group
✕ Audibly loud
It draws in warm room air, cools it and returns it — the waste heat leaves through the window hose. Real cooling, not just moving air around.
What heats a room up — the factors
The check scores the four factors from 0 to 100. The higher the total, the higher the overheating risk:
| Factor | Biggest driver | Effect |
|---|---|---|
| Location | Attic / loft | strongest — roof rooms heat up extremely |
| Window direction | South / West | very strong — direct afternoon sun |
| Window area | large / floor-to-ceiling | strong — more glass, more solar gain |
| Insulation | old building / poor | medium — heat stays in the room longer |
What helps — in the right order
Order matters: first block the sun, then ventilate, then actively cool. An air conditioner in an unshaded south-facing attic room fights the incoming sun — with external shading or a thermal blind the cooling demand drops sharply. Only then does the risk decide whether a fan, an air cooler or a portable air conditioner is the answer.
Frequently asked questions
Why does my room get so hot?
The biggest factors are location (attic and top floors heat up the most), window direction (south/west lets in the most sun), large window areas and poor insulation. An attic room with a big south window in an old building has the highest risk.
What helps most against an overheated room?
In this order: first block the sun (external or a thermal blind), then ventilate at night and early, then actively cool — a fan at low, an air cooler at medium, a portable air conditioner at high risk.
Do I need an air conditioner in an attic room?
Often yes: attic rooms heat up the most. The sensible combination is shading plus a portable air conditioner with enough BTU — size one step up for an attic.