The capacity of a dehumidifier is the maximum amount of water that can be extracted at a given temperature and RH. For example, if a dehumidifier is rated at 40L, 20C and RH60%, that means it can extract 40L of water per day under constant conditions of 200C and RH at 60%(What is Relative Humidity?).
Dehumidifiers are tested in laboraties by keeping a constant temperature and RH and then measuring the amount of water that is collected over 24 hours.
Dehumidifiers can extract a lot more water and higher temperature and RH. For this reason, many manufacturers like to use extraction rates at 300C and RH80%, to make the extraction rates seem higher. However, measuring capacity and such high temperature and RH is unrealistic. With a dehumidifier running in a room, the RH drops and room RH will not stay at 80% for long.

To compare capacity among dehumidifiers, make sure you get the capacity at the SAME temperature and RH.

The water collected from the dehumidifier (condensate) is actually quite usable as it has a low mineral content compared to tap water. You can water your plants, clean the car or mop the floor with it, flush the toilets, take a shower….and so on! However, it is not advisable to drink the condensate directly. Some impurities may be present in the dehumidifiers during the dehumidification process.

It is quite surprising how much water can come out of dehumidifiers. Our dehumidifiers can extract 28L of water a day at 200C and 60% RH. Drying your laundry alone can yield 3-5L of water (How much water does clothes absorb after you wash them?).

  • (a) Room Size:
    With a larger room, you not only need a larger capacity dehumidifier and also a dehumifier with a larger fan. Dehumidifiers can only dry the air it can circulate. If the fan is weak, it may not be able to circulate the air in the entire room.

  • (b) Target RH:
    If the target RH is 60% versus 50%, you may not need as powerful a dehumidifier.

  • (c) Number of people in the room:
    We exhale about 400-600mL of moisture in a day, just sitting down being inactive! If you have 10 people in a space you are trying to keep dry, you will have additional moisture load to take into account!