A dehumidifier’s liters-per-24h figure is real, but it’s measured under a condition your room probably doesn’t match.
The reference condition manufacturers rarely state
None of the dehumidifiers we’ve reviewed — Cecotec’s BigDry 2000, COMFEE’s Aqua Dry 10, Bosch’s Dry 4000 — publish the exact temperature and humidity their extraction figure was measured at. The industry-standard reference is commonly around 30°C (86 °F)/80% RH, conditions most homes don’t sit at.
What that means for a cold room
A cellar or an unheated bedroom at 15–18°C (59 to 64 °F) will see a compressor dehumidifier extract noticeably less than its rated figure, and some compressor units struggle or ice up below a certain temperature entirely — check for a stated low-temperature or defrost feature if this applies to you.
Match rated capacity to the actual problem, generously
Cecotec’s BigDry 2000, at 300 ml/24h, suits a wardrobe or small enclosed space, not a room. Bosch’s Dry 4000, at 16 L/24h, suits an actual damp room. If your space runs cold, consider sizing up from the room-only calculation to compensate for reduced real-world extraction.
What we would not do
Compare two dehumidifiers’ liters-per-day figures as if they were measured identically. Neither publishes its test condition, so a stated figure is a useful but imprecise guide, not an exact promise for your specific room.
The questions that keep coming up
Why does my dehumidifier seem to extract less than its rated figure?
Almost certainly temperature. Manufacturers typically measure extraction at around 30°C (86 °F) and 80% relative humidity — a warm, genuinely damp test condition. A cool 18°C (64 °F) room will show meaningfully less extraction for the same rated unit.
Last reviewed 24 August 2026