If you're trying to beat indoor dampness – especially in cold weather – you might be scratching your head over whether a dehumidifier is the answer and which one to choose. Do they really live up to their claims? How do they cope in winter when it's harder to extract moisture from the air?
We lab test dehumidifiers to find out which ones really work so you can choose the best one for your needs. Here's how we go about it.
CHOICE maintains a highly professional NATA-accredited laboratory and the vast majority of our product testing is done in-house. However, some tests – including dehumidifiers – demand particular expertise and equipment that we don't have, so in these cases we engage an accredited external lab to do the testing according to our requirements.
With so many models to choose from, what makes us choose one dehumidifier to test over another? Like with most of our product testing, our aim is to test the most popular models on the market and what you're most likely to see in stores.
We survey manufacturers to find out about their range of dehumidifiers, we check market sales information, and we also check for any member requests to test specific models. We then put together a final list of products that goes to our buyers. They then head out to retailers and buy each product, just as a regular consumer would. We do this so we can be sure the machines haven't been 'tweaked' in any way for better performance.
Water removal and energy efficiency
The dehumidifiers are set up in a temperature- and humidity-controlled test chamber measuring 5m x 6m x 2.4m, about the size of a living room. For each model, the lab measures the amount of water removed in three tests at different temperature/humidity combinations that reflect damp winter climates:
- 8°C / 90% relative humidity
- 12°C / 75% relative humidity
- 16°C / 65% relative humidity.
We've found the best-performing dehumidifiers remove more than twice the volume of water compared with the worst models at the coldest temperatures.
Cold, humid conditions present a worst-case scenario for most dehumidifiers, as they usually use refrigeration technology. It's easier for a refrigeration dehumidifier to extract moisture from warm air than from cold air (which is why manufacturers usually quote removal rates at conditions that make their machines look the best – typically 30°C and 80% relative humidity), because it's easier for them to cool hot air (in order to condense the water from it) than to further cool air that's already cold.
We've found the best-performing models remove more than twice the volume of water compared with the worst models at the coldest temperatures
To see how a desiccant dehumidifier compares with a refrigeration model in hot humid conditions, we've conducted tests in 30°C and 80% relative humidity, and also 25°C and 70% relative humidity, using desiccant models and refrigeration models.
All performed OK, but the refrigeration models could extract up to four times as much water in hot conditions as they did in cold conditions.
When measuring the water removal, the lab also measures the energy consumption of the dehumidifier. From this we can calculate how many millilitres of water the model extracts from the air per watt of electricity used, and therefore how energy-efficient the model is in comparison to others we're testing. We also measure how well the claims of the dehumidifier match up to our findings.
Ease of use
The lab testers assess each model for ease of accessing and emptying the water tank, quality of instructions and labels, using the controls, mobility of the unit and how easy it is to clean.
We measure the noise of the unit while it's running (these results are comparative only – what you actually hear depends on the environment). Most measure upwards of 50dB, which is enough to potentially be annoying if you're trying to watch TV or sleep.
These are the approximate per-hour cost of running the unit and the electricity cost for the unit to extract 10 litres of water. The latter figure often shows that a model that uses less power, but is slow to extract water, can cost the same to run as a model with higher consumption but faster extraction.
Occasionally we test an unusual model or type of dehumidifier that demands a different approach to testing.
For example, we tested a small commercial unit, the Ecor Pro DH800, which is designed to be permanently installed. It doesn't have a water collection tank or drainage hose, but instead dries the air via a desiccant, vents the moisture-laden air outdoors, and blows dry air back in the room.
This meant the lab couldn't simply measure the collected water to assess its performance during the usual tests. Instead, they carefully measured the temperature and humidity of the three air streams (the air inlet, the wet air outlet and the dry air outlet), and used this data to calculate the total amount of water removed from the test room's air.
We also tested DampRid, a popular chemical-based moisture absorber. It works much more slowly than dehumidifier appliances, and isn't really meant to dry out a whole room – it's mainly for use in small enclosed spaces such as wardrobes and closets.
So in addition to the usual tests, the lab built a sealed cube, three cubic metres in volume, filled with humid air at approximately 80%RH, to simulate a damp closet. The DampRid container was put inside and the internal air monitored for temperature and humidity over about 60 hours.
The CHOICE Expert Rating (or overall score) for dehumidifiers is made up of:
- water removal (30%)
- claimed water removal (20%)
- energy efficiency (30%)
- ease of use (20%).
Testing dehumidifiers requires a very specific laboratory, as described above. While CHOICE does have high quality thermal laboratories, we don't have a lab suited to this particular testing; it would be very expensive to construct and maintain. So instead, when we review dehumidifiers we send them to a qualified external lab.
Stock images: Getty, unless otherwise stated.