🗓 Updated July 9, 2026 · EcoBack editorial team
BTU (British Thermal Units) measures an air conditioner's cooling power. Too few and it can't keep your room cool; too many wastes money and makes more noise. Here's the simple version.
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 PAC N90 ECO Silent
Monoblock test winner at Stiftung Warentest, silent mode, R290 refrigerant.
✓ Quietest monoblock in its group
✕ Pricier than the value pick
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
Klarstein Kraftwerk Smart 12K
Strongest cooling of its group in public comparisons.
✓ Strongest cooling of its group
✕ Audibly loud
De'Longhi Pinguino PAC EX105
Strong cooling, often in the test-winner line.
✓ Strong cooling, good efficiency
✕ Big & heavy
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These are the models US reviewers keep picking — compiled from public tests, not tested by us. Prices change; check the current price on Amazon. Illustrations, not product photos.
Midea Duo MAP14HS1TBL
Dual-hose inverter — it takes its exhaust air from outside instead of from your room, which is the flaw single-hose units have. Repeatedly the overall pick in US tests.
Whynter NEX ARC-1230WN
Rated for noticeably larger rooms than the usual portable unit.
Black+Decker BPACT14WT
The common budget recommendation; US reviewers note it struggles in big or west-facing rooms.
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.
BTU by room size
A good rule of thumb is roughly 350–400 BTU per m². Use this chart:
| Room size | Recommended BTU | Typical room |
|---|---|---|
| Up to 15 m² | 7,000–9,000 BTU | Small bedroom, study |
| 15–25 m² | 9,000–12,000 BTU | Bedroom, home office |
| 25–35 m² | 12,000–14,000 BTU | Living room |
| 35 m²+ | 14,000+ BTU / monobloc | Open-plan, large lounge |
Add BTU if…
- The room gets strong afternoon sun — add ~10%.
- It's a top-floor or attic room — heat rises, size up.
- Several people or a kitchen/electronics in the space — each adds heat.
- High ceilings (above ~2.7 m) — you're cooling more air volume.
Don't oversize "to be safe"
A too-powerful unit short-cycles (blasts, stops, repeats), which cools unevenly, runs louder, and costs more. Match the room and only bump up for the factors above.
Know your number? Filter portable ACs by BTU on Amazon.de:
See portable ACs on Amazon.de →For a bedroom, also check the noise rating — see best portable AC for a bedroom. Got tilt-and-turn windows? Read how to vent a portable AC with tilt-and-turn windows first.