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Dehumidifiers and condensation control

Dampness is a serious problem in many New Zealand homes. A survey by Statistics NZ found almost half of renters battle excess moisture. Mould and dust mites thrive in these conditions, which can lead to allergies, asthma and severe respiratory illnesses.

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If you've got a problem with condensation, the first thing you need to do is consider where the water is coming from. Before buying a dehumidifier, we think it’s crucial your home has adequate heating and ventilation. Tackling the sources of dampness is the only way to effectively stop mould.

Controlling condensation

Where does the water come from? Here are some of the common sources of moisture in your home.

  • Cooking: 3.0L per day
  • Clothes washing: 0.5L per day
  • Showers and baths: 1.5L per day (per person)
  • Dishes: 1.0L per day
  • Clothes drying (unvented): 5.0L per load
  • Gas heater (unflued): up to 1.0L per hour
  • Breathing, active: 0.2L per hour (per person)
  • Breathing, asleep: 0.02L per hour (per person)
  • Perspiration: 0.03L per hour
  • Pot plants: as much as you give them

Improving condensation problems

  • Keep rooms ventilated and warm during winter - at least 7°C warmer than outside temperatures. Install heavy curtains and draw them at night: it helps keep the home warm and reduces the number of cool surfaces for water vapour to condense on. Leave windows closed on damp days.
  • Always use close fitting lids on pots when cooking and fit extractor fans over the cooktop or stove, and in the bathroom (these must be ducted to the outside).
  • Dehumidifiers have often been teamed with unflued LPG heaters. One spews out moisture (and other contaminants) while the second mops up the moisture. No, no, no. It’s not the dehumidifier that’s the problem here – it’s the unflued LPG heater. Their exposed flame is a fire risk and they fill the house with water and other harmful contaminants. Don’t use them. Use cheaper to run and safer electric heaters.
  • A shower dome can collect condensation from showers and send it down the drain.
  • Use a cupboard heater in problem wardrobes. A ventilation grille in the top of the wardrobe will also help.
  • Vent clothes dryers to the outside and don't hang clothes inside to dry. Close doors when cooking, showering or using the dryer, to limit the spread of moist air.
  • Limit the number and size of pot plants in the house.
  • Check the ground under your house is dry. If it's wet, cover with polythene (if feasible), taping the joints, and ensuring a tight fit around piles. Check that drainage systems are diverting water away.
  • Fix any leaks in the roof or around windows.

Signs of excess moisture

  • Musty smells in rooms that are closed for any period of time.
  • Damp or mouldy clothes in wardrobes.
  • Mould or mildew forming behind paintings, mirrors, etc.
  • Stains or watermarks on ceilings or walls.
  • Mouldy ceilings and walls.
  • Problems with areas of rotting wood in the structure of your house.
  • Mould under your house.
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