When you’re browsing dehumidifiers, either online or in store, the number that sticks out is rated capacity.
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Separate from tank size, rated capacity is the claimed maximum amount of water a dehumidifier can remove each day – usually ranging from 10L (a smaller model) up to 50L (a whopper).
Dehumidifier labelling typically shows only those maximums. But these extraction rates are achieved in conditions far removed from what you’d get over a Kiwi winter.
Realistic test conditions
Manufacturers test their dehumidifiers in optimal conditions – usually 30°C at 80% relative humidity (RH). However, it’s unlikely you’ll find any flats in Otago with these balmy conditions in July!
That’s why we test dehumidifiers in conditions you’d expect in Kiwi homes over winter – ranging from 8°C and 90% RH to 16°C and 65% RH.
We got very different results in our testing.
On average, the dehumidifiers extracted less than 30% of their claimed maximum capacities after 24 hours, with tanks emptied as soon as they were full. The results were worse in our low temperature test (8°C), even at 90% RH.
The Goldair GD350 got closest to its stated daily extraction rate of 8L, collecting an average of 5.7L a day. Being a desiccant model, it does a good job of removing moisture even in cold conditions when most refrigerant dehumidifiers struggle. But it costs nearly three times more to run than the average refrigerant model.
The dehumidifier with the highest claimed extraction rate – the Mitsubishi Electric MJ-EV38HR-A – extracted a daily average of 6.8L of moisture, being only 18% of its claimed 38L maximum. This model is one of the most expensive in our database, costing about $1,500.
While maximum capacity claims can be overly optimistic, a dehumidifier taking several litres of moisture out of the air will certainly improve the health of a damp home.
Water tank woes
Not only are manufacturers’ rated capacities a little optimistic, their stated tank sizes are usually slightly off the mark too.
We measure tank capacity as being up to the point the dehumidifier switches itself off after detecting it’s full – not just the tank’s total capacity. Usually, this difference is several hundred millilitres.
In addition, tank capacity is always much less than the amount of water a dehumidifier can extract each day. If one of the 30L models really did extract 30L of water per day, you’d be emptying the tank (5L on average) every four hours.
Our view
We’d like to see dehumidifier manufacturers be more realistic about their water extraction rates. The best outcome would be for them to measure the daily capacity of their dehumidifiers at several different temperatures and humidities, labelling them with their average capacities.
To find out how well the dehumidifier you’ve got your eye on performs in Kiwi conditions, check out our database of 23 tested models.
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