How to read a dehumidifier's litres per day
The big number on the box is how much water the machine pulls out of the air in a day under one set of test conditions. Change the conditions and the number changes a lot, so a "20 litre" machine may remove far less than 20 litres in your bedroom.
One machine, six different numbers
Meaco publishes how much water its 20L Low Energy model removes at several temperatures and humidities: the 30°C/80% figure under "Performance" and the rest in the "Water removal" table under "Specification" on its product page (checked 30 October 2026). It's a useful example because it shows how much the conditions matter.
| Room temperature | Relative humidity | Litres per day |
|---|---|---|
| 30°C | 80% | 20.38 |
| 20°C | 80% | 13.74 |
| 30°C | 60% | 13.27 |
| 20°C | 60% | 8.48 |
| 10°C | 80% | 5.86 |
| 10°C | 60% | 2.52 |
The "20L" in the name is the top row: a hot, very humid room. A temperate living room at 20°C and 60% gets well under half of that. A cold room at 10°C gets about an eighth.
What to look for
- The test conditions next to the number. If the box or listing doesn't say what temperature and humidity the figure was measured at, the number can't tell you how the machine will do in your home.
- A figure near your room's conditions. If your damp room is a cool bedroom, look for a rating at 20°C or below, not 30°C.
- Different models compared at the same conditions. Comparing one brand's 30°C/80% figure with another's 20°C/60% figure compares the test rooms, not the machines.
There is no single conversion that works for every model. The drop from hot to cool differs from machine to machine, which is why this guide doesn't give you a rule of thumb to divide by.
Cold rooms
The table shows the pattern for this compressor model: as the room gets colder, it removes much less water. Desiccant dehumidifiers work differently. Whichever type you look at, ask for its figure at the temperature your room actually sits at.
Before you buy one at all
A dehumidifier treats damp air. It doesn't fix where the water comes from. Clothes drying indoors, a dryer venting into the room, a bathroom with no working fan, or water getting in through the building can keep adding moisture and limit how much a dehumidifier can do. The four questions sort out which of those applies first. Keeping indoor humidity below about 60% is the usual target (US EPA); a cheap hygrometer will tell you whether you're above it before you spend more.
Sources
Each source below was opened and checked against this page on 30 October 2026.