Dehumidifiers remove humidity from the air in the area of the machine. Removing humidity may improve comfort in the home but also helps keep wood in the home from swelling or warping and prevents the build-up of mould and mildew in the home. Dehumidifiers are commonly used in basements rather than the above-ground living quarters. A study of the effectiveness of dehumidifiers was performed by the Canada Mortgage and Housing Corporation in 2004.
Relative humidity is a measurement of the amount of moisture in the air relative to the amount of moisture the air is capable of holding at that temperature. A relative humidity of 50 per cent means the air is holding half the moisture it possibly can at that temperature. Warmer air is capable of holding more moisture than colder air. The action of the dehumidifier lowers the relative humidity or the amount of moisture in the air without effecting the temperature of the air.
By changing the water that is in the vapour state in the air into a liquid state, the dehumidifier can accumulate the moisture for disposal. More effective dehumidifiers remove more water from the air. The study by the Canada Mortgage and Housing Corporation indicated that some dehumidification operations removed as much as 0.6 litres of water per hour of operation while others removed as little as 0.2 litres per hour.
The dehumidifier converts moisture in the vapour form into liquid water. This water accumulates in a tank that is dumped as necessary. Careful operation, keeping the dehumidifier operating by dumping the water tank to prevent shutdown, improves the operational efficiency of the device. Other factors include the size, capacity and model of the dehumidifier.
The Canadian test found that the homes with dehumidifiers had lower basement relative humidity than homes without humidifiers during all months except during the winter. The relative humidity levels on the main floor of the home were not affected during the period. This was explained by greater air circulation with the outdoors occurring upstairs compared to the basement. The main floor humidity closely followed the outdoor humidity levels. The humidifiers lowered the moisture level in the wood of the basement from 10 per cent during the control period to between 7 and 8 per cent when dehumidifiers were used. The test indicated that more than 50 per cent of the homes saw improved or lowered relative humidity levels with the installation of a dehumidifier.