Why dehumidifier claims are unrealistic

The latest cold snap has resulted in scores of Kiwis dragging their dehumidifiers out of storage to battle the winter damp, but do they live up to their lofty claims?

Condensation on a window

When you’re browsing dehumidifiers, either online or in store, the number that sticks out is rated capacity.

Usually ranging from 10L (a smaller model) up to 30L+ (a whopper), rated capacity is the claimed rate of water a dehumidifier can remove per day. If you purchased a 30L dehumidifier that sucked up this much moisture, your home would likely never have any damp problems again.

However, our testing has found these figures are generally pie in the sky and your dehumidifier will likely never get anywhere near these numbers.

So, what’s the problem? It comes down to how manufacturers come up with their claims.

Dehumidifier claims vs reality

Manufacturers test their new dehumidifiers in optimal conditions, usually about 30°C at 80% relative humidity (RH). However, we think it’s unlikely you’ll find any flats in Otago with these balmy conditions in July!

In comparison, we test dehumidifiers to conditions you’d expect in Kiwi homes over winter – ranging from 8°C and 90% RH to 16°C and 65% RH. Once you dial things back to real-world conditions, dehumidifier performance starts to suffer.

After assessing all the tested dehumidifiers in our database, the average amount of water in their tanks after we left them running for 24 hours was only 37% of claimed capacity. The results were slightly worse at the lower temperature (8°C) – on average they only removed 35% of the claimed amount of water over 24 hours, even with humidity at 90%.

Only one model, the desiccant Dimplex GDDEKD9, managed to meet and exceed its posted extraction rate (that said, its claimed rate was a more realistic 9L).

Collection tank woes

Not only are manufacturers’ moisture-removal claims off the mark, their posted tank sizes are usually inaccurate. We measure tank capacity as being when the dehumidifier switches itself off after detecting it’s full, not just the tank’s total capacity. Usually this difference is a few hundred millilitres, which could be a few hours’ of runtime you’re missing out on. While not as big of an issue as the capacity claims, we think this type of claim short-changes the performance a consumer could expect.

Our view

We’d like to see dehumidifier manufacturers post more realistic capacities. Claiming a model can remove 30L just isn’t achievable in this country. The best outcome for consumers would be for manufacturers to test and note rated capacities at several different temperatures and humidities.

Until then, to find how much moisture the dehumidifier you’ve got your eye on can really suck up, check out our database of 19 tested models.

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