Static sparks, harsh air and plants that dry out quickly? It may be because the indoor air is too dry. Here we go through what dry air is, how to recognise it and how to raise the humidity.
Short answer: Dry indoor air means the relative humidity is below about 30 percent. It is most common in winter when heated air becomes dry. You raise the humidity by airing out in moderation, drying laundry indoors, keeping plants or using a humidifier. Aim for 30 to 60 percent.
What counts as dry indoor air?
Air is considered dry when the relative humidity is below about 30 percent. The guideline for comfortable indoor air is 30 to 60 percent. The further below 30 percent the level drops, the more the dryness shows on both feel and materials.
Signs of dry air
- The air feels harsh and a little scratchy.
- More static electricity, such as small sparks when you touch things.
- Wooden floors, furniture and instruments can shrink and crack.
- Potted plants dry out faster than usual.
Why does indoor air get dry?
The most common cause is heating during winter. Cold outdoor air contains little moisture, and when it is heated the relative humidity drops. Good ventilation that exchanges the air often can also contribute in winter, because the humid indoor air is replaced with dry outdoor air.
How to raise the humidity
- Air out for shorter periods. Long airing sessions in winter exchange the moisture for dry outdoor air.
- Dry laundry indoors and let the moisture evaporate into the room.
- Add potted plants or a bowl of water near a heat source.
- Use a humidifier if the level is often far below 30 percent.
Do not overdo the moisture
It is possible to raise the humidity too much. If it stays above 60 percent the risk of condensation and, over time, moisture and mould increases. If a room becomes too damp, a dehumidifier lowers the relative humidity instead. The goal is to stay within 30 to 60 percent. To understand how moisture moves through the house there is more in the guide on moisture in the home.
Measure with a hygrometer
The surest way to know whether the air is actually dry is to measure it. A hygrometer shows the relative humidity in percent. Place it in a room you use a lot and read it at different times of day. Here is how to do a moisture measurement at home, and more advice on the indoor climate is in the guide on air quality at home.
Frequently asked questions
What counts as dry indoor air?
Air is considered dry when the relative humidity is below about 30 percent. The guideline for comfortable indoor air is 30 to 60 percent.
What causes dry indoor air?
Usually heating during winter. Cold outdoor air contains little moisture, and when it is heated the relative humidity drops and the air feels dry.
How do I raise indoor humidity?
Air out for shorter periods, dry laundry indoors, keep potted plants or a bowl of water near a heat source. A humidifier can add moisture if the level is often very low.
Can you raise the humidity too much?
Yes. If it stays above 60 percent the risk of condensation and moisture increases. Aim for 30 to 60 percent and measure with a hygrometer.
