Relative humidity (RH) is the percentage of moisture in the air compared to the maximum moisture the air can hold at a given temperature. RH helps determine the comfort and health level of an indoor environment, as humidity levels that are too high or too low can have negative effects on human health and the condition of buildings.
How relative humidity works
At higher temperatures, the air can hold more moisture, so the same humidity level results in a lower RH value.
At lower temperatures, the air can hold less moisture, so the same amount of moisture can result in a higher RH value.
Example:
In a room at 25°C with a relative humidity of 50%, the air is half saturated with moisture. If the temperature drops, for example to 15°C, the air can become saturated and excess moisture condenses (e.g. condensation on windows).
Optimal indoor relative humidity
ASHRAE and other health organizations recommend that indoor relative humidity be between 30% and 60%, as follows:
- Between 30-50% in the winter months: Helps prevent condensation on windows and reduces respiratory problems.
- Between 40-60% in the summer months: Provides a more comfortable feeling and reduces the risk of mold growth.
Dangers of too high humidity (>60%)
- Growth of mold and dust mites, which can cause allergies and respiratory diseases.
- Bacteria and viruses spread more quickly.
- Structural damage caused by moisture, such as damage to walls, ceilings or furniture.
- Condensation on windows, which can promote rotting of wood or other materials.
Dangers of too low humidity (<30%)
- Dry skin, eye and throat irritation.
- Dryness of the respiratory tract mucous membranes, which makes the body susceptible to infections.
- Static electricity, which can cause discomfort and damage electronic devices.
- Drying of wooden materials (e.g. flooring, furniture), which can lead to cracks and warping.
Humidity control
The following tools and techniques can be used to maintain the appropriate humidity:
Hygrometer: A simple device that helps you accurately measure humidity. Many modern thermostats also have a humidity measurement feature.
Dehumidifier: If the humidity is too high, a dehumidifier removes excess moisture from the air.
Humidifier: If the humidity is too low, a humidifier adds the necessary moisture to the air.
Ventilation: Frequent ventilation can reduce humidity, especially in the bathroom and kitchen.
Plants: Some houseplants can naturally reduce or increase humidity, depending on how much water they evaporate.
Seasons and humidity
In winter: Heating systems often dry out the air, so humidification may be necessary.
In summer: Due to higher outdoor humidity, dehumidification is important, especially with air conditioning.
Summary
Measuring and controlling relative humidity is key to maintaining an optimal indoor environment. Proper humidity helps prevent health problems, increases comfort, and protects the condition of buildings and furniture. With the help of hygrometers, humidifiers, and dehumidifiers, we can easily monitor and adjust humidity levels to keep our indoor environment healthy and pleasant.