Proper home ventilation prevents moisture damage and mildew

Hamburg  - Ventilating a home was no problem in the past because even when windows were kept shut, there was a constant exchange of air through poorly insulated exterior walls, joints, and cracks.

This uncontrolled ventilation wasted a lot of energy, though, and made the home's occupants turn up the heat. To save energy, buildings in Germany have been better insulated and equipped with modern windows in recent years.

But the new, airtight windows with heat-insulating glazing have a negative side. "Unless ventilation methods are changed, air moisture caused by showering, cooking, and washing isn't drawn out of living quarters, kitchens, and bathrooms," noted Dirk Petersen, who works for Hamburg's consumer advice centre.

The higher relative humidity that results, he said, could cause condensation on the inner surfaces of cold external building components - particularly in poorly insulated old buildings - which promotes the growth of mildew.

This is not the only reason that proper ventilation is essential for the health of a home's occupants. If closed rooms are insufficiently aired, they develop excessively high concentrations of carbon dioxide (CO2), a gas that humans exhale. Too much CO2 in the air impairs wellness and working capacity.

Proper ventilation is also necessary to rid room air of harmful substances such as cigarette smoke or toxic fumes from paint or furniture.

The more airtight the building, the more important it is to ventilate regularly. "If you ventilate the traditional way, by opening windows, you should open them completely several times a day all year round," Petersen advised.

Rooms should not be aired out by opening windows merely a crack. Cross ventilation, in which windows and doors are opened in rooms opposite one another, improves the air markedly. So does completely opening individual windows for a short time.

"The relative humidity of room air should be between 40 and 60 per cent," Petersen said. The percentage can be measured with an instrument called a hygrometer. Less than 40 per cent is uncomfortable, Petersen noted, and more than 60 per cent allows mould, mildew and house mites to multiply.

Most of the energy consumption in energy-saving homes can come from heat loss due to improper ventilation. And insufficient ventilation can result in excessive humidity.

"To prevent (moisture) damage, new buildings as well as renovated old buildings should be equipped with a home ventilation system," advised Jens Knissel, a staff member at the Darmstadt-based Institute of Living and Environment (IWU).

There are various types of automatic systems. "A simple solution for controlled home ventilation is a used-air unit," said Michael Conradi, a member of the Berlin-based HEA Group of Experts on Efficient Energy Use.

This system has a central ventilator, or several decentralised ones, that extract air from the rooms most affected by odours and water vapour: the kitchen, bathrooms, and toilets. Fresh outside air flows in through ducts in the building envelope.

The fresh air flows constantly from the living and sleeping quarters to the humid rooms. Units with heat recovery are especially effective. They have heat exchangers able to take heat from the warm, used air and transfer it to the incoming air - or to the home's tap water. (dpa)

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