Checklist

Before buying a dehumidifier you should do everything possible to reduce the causes of dampness. Underfloor water barriers, improved insulation as well as kitchen and bathroom ventilation are all good stuff. But for most homeowners these are longer-term projects – and most are impossible if you are renting.

A dehumidifier starts improving your home environment the moment you switch it on. And you can take it with you if you move house.

Features

If you're thinking of buying a dehumidifier, consider these features:

Low temperature effectiveness
You can get excessive moisture in the air at high and low temperatures, and will want a machine that can deal with both. However, makers usually give water removal rates at conditions which make their machines look the best, typically 30°C and 80 percent relative humidity (RH).

For example, a machine may claim to remove 16 litres a day at 30°C and 80 percent RH. The figures sound impressive, but are misleading for anyone wanting to deal with winter condensation, when temperatures get below 15°C. Try asking for figures at 10°C and 15°C, although they will not always be available.

Using a heater and a dehumidifier together will heat a cold and damp room more quickly and cheaply than using just a heater.

Mobility
Look for a model with good castors and a handle or hand-grips to ensure easy movement. Models can range in weight from 10 to 25 kilograms. If you have stairs, shop around for a model that's not too heavy for you. If space is a concern, check the dimensions. Some take up much less space than others.

Tank
There is usually a trade-off between mobility and size. Small water-collection tanks make a dehumidifier more compact, lighter and easier to carry around. But if the tank is too small, you'll have to empty it several times a day.

Models with larger tanks won't need to be emptied as often but can take up more floor area, and a big tank full of water can be difficult to manoeuvre to the emptying point.

Models with a front tank are easier to empty. Check that it is easy to remove, and big enough to hold at least five litres of water. Some models have a drain hose adaptor, which removes the water as it's collected, so it can be poured straight down a drain.

Controls and labels
Make sure they are easy to see, understand and use. An adjustable humidistat allows you to set humidity levels.

Rotary dial humidistats with no precise markings make it hard to find the actual humidity level. If this is particularly important (as it may be for some people with allergies, for example) you can buy a humidity gauge to check humidity levels. See www.thermometer.co.nz.

Noise
Most dehumidifiers make upward of 50 decibels (dBA) of noise - enough to be annoying if you're trying to watch TV, hold a conversation or sleep. (A reasonably quiet fridge makes about 39-40dBA.)