Our dehumidifiers test found actual performance is much lower than the manufacturers claim. So we sent our test results to the manufacturers to see what they had to say about it.
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Visit an appliance store and you’ll find many dehumidifiers claiming to remove 10-20L a day, with some models rated at upwards of 30L. That’d be great if it were realistic – removing 30L water from the air each day would leave even the dankest Dunedin flat bone dry.
The trouble is manufacturers base their water extraction claims on tests conducted at about 30°C and 80 percent relative humidity (RH). Unless you live in the Amazon, those conditions are nothing like the winter climate in your home. We tested dehumidifiers in conditions ranging from 8°C and 90 percent RH to 16°C and 65 percent RH, which are more typical of a New Zealand winter, and found actual performance is much lower.
On average, the amount of water removed over 24 hours at our test at 16°C was less than a third of the headline figure claimed on the box. Among dehumidifiers rated at 20L a day (the most common size in our round-up), the average amount of water in the tank after we left them running for 24 hours was 6.0L, with the top-performing 20L model managing 7.5L.
The results were even worse at low temperatures (8°C): on average they only removed 3.3L of water over 24 hours, even with humidity at 90 percent. The upshot is if you’re buying a dehumidifier to use in an unoccupied, unheated room during winter, the only way you’ll get a good indication of its performance is by using our test results.
We sent manufacturers and distributors the performance data from our test, and asked them to comment on the disparity between our results and their claims. The responses ranged from defensive to constructive.
In general, most said they base their results on tests at about 30°C and 80 percent RH because this is the “industry standard” used worldwide for rating dehumidifiers, and adopted by most manufacturers.
However, some acknowledged these conditions do not reflect the reality in Kiwi homes during winter, and took a more proactive stance. Yale Prima, which distribute Moretti dehumidifiers, said its “currently developing a performance table listing various weather combinations” and is looking at incorporating this information on its packaging. We’d like to see all manufacturers follow this example.
CDB Media, which distribute Goldair, Evantair, Celsius, Noveau and Stadler Form, include the following statement in its user guides: “where you do not have [high] humidity and high temperatures the extraction levels will be lower.” It also addresses this issue in some of its catalogues, though in our view this doesn’t compensate for the fact that claims on the box are potentially misleading.
Black Diamond Technologies (BDT), the distributor for Mitsubishi Electric, also acknowledge in their user manuals and on their website that their dehumidifiers will “collect less water in winter” and provide a chart showing water removal at lower temperatures. But BDT managing director Daryl Rochester disagreed that test results at lower temperatures would be helpful. “BDT rejects the assertion by Consumer that temperatures of 8, 12 or 16[°C] are relevant to typical New Zealand homes,” he said. He claimed BDT’s data indicates the average temperature in New Zealand homes in mid-winter is “around 19°C”.
This view isn’t shared by Doctor Lucy Telfar Barnard, University of Otago Housing and Health Research Programme senior research fellow. Dr Telfar Barnard said the average winter temperature indoors is nowhere near 19°C, especially in the cold, damp rentals that rely on dehumidifiers.
She cited the Building Research Association of New Zealand’s (BRANZ) Home Energy End Use report, based on a study of 400 houses between 1997 and 2005, which found the average winter temperature over 24 hours was only 15.5°C in living areas and 13.9°C in bedrooms.
Dr Telfar Barnard said although there’s been progress in improving the levels of insulation and heating in New Zealand homes, there’s nothing to indicate indoor temperatures would have jumped dramatically in the past 11 years. The other issue is dehumidifiers are commonly used in unoccupied, unheated rooms, which are likely to fall below 10°C during winter.
Consumers deserve a more realistic indication of dehumidifier performance. Manufacturer’s claims need to be based on test conditions relevant to New Zealand’s climate. We think the industry should adopt a testing standard that shows performance at a range of temperatures and humidity levels.
In our view, it’s misleading to publish data based on conditions that are nothing like the average New Zealand home.
Report by George Block.
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