Does the air at home feel dry and does your nose start to itch as soon as the heating comes on? In winter the indoor humidity drops, while some rooms can get too damp. Here is how to keep a comfortable level all winter.
Short answer: In winter the indoor humidity often falls to 20 to 30 percent, because cold outdoor air is heated up and becomes dry. Aim for 30 to 60 percent relative humidity. Air out in moderation, avoid over-drying the air and keep track with a hygrometer.
Why does indoor air get dry in winter?
Cold winter air contains very little water vapour. When the cold outdoor air comes in and is heated, it keeps the same amount of water, but because warm air can hold much more moisture the relative humidity drops. The colder it is outside and the warmer you keep it indoors, the drier the air feels.
What humidity should you have indoors in winter?
The guideline is 30 to 60 percent relative humidity, and in winter many end up in the lower part, around 30 to 40 percent. Below 30 percent the air starts to feel harsh and static electricity becomes more common. Above 60 percent the risk of condensation and moisture increases instead. Aiming for the middle of the range gives both comfortable air and a lower risk of moisture problems.
How to raise humidity when it is too low
- Air out for shorter periods rather than for a long time, so you do not exchange all the moisture unnecessarily.
- Let laundry dry indoors and add a few potted plants.
- Place a bowl of water near a heat source so moisture evaporates slowly.
- Use a humidifier if the level is often very low during winter.
Watch out for condensation and too much moisture
While the air in the living room can be dry, other rooms easily become too damp in winter, such as bathrooms and bedrooms where we breathe out moisture at night. That moisture can settle as condensation on cold windows. If a room is consistently too damp a dehumidifier can lower the relative humidity. Read more about moisture in the home and about mould to understand the risks.
Common winter mistakes
- Over-drying the air with high heat and little moisture, so it drops far below 30 percent.
- Not airing out at all for fear of the cold, which lets moisture and carbon dioxide build up.
- Just guessing. Without measuring it is easy to think the air is dry when it is actually too damp, or the other way around.
Keep track with a hygrometer
An inexpensive hygrometer shows the current humidity in percent and makes it easy to know which way to steer. Place it in a room you use a lot and read it at different times. There is a step-by-step guide on measuring moisture at home, and more advice on the indoor climate in the guide on air quality at home.
Frequently asked questions
What is normal indoor humidity in winter?
Around 30 to 40 percent relative humidity is common in winter. The year-round guideline is 30 to 60 percent, and in winter you often end up in the lower part because heated air becomes drier.
Why does the air get so dry in winter?
Cold outdoor air contains little water vapour. When it is heated indoors the relative humidity drops, because warm air can hold more moisture. That is why indoor air feels dry during winter.
How do I raise indoor humidity in winter?
Air out for shorter periods, let laundry dry indoors, keep plants or place a bowl of water near a heat source. A humidifier can add moisture if the level is often very low.
Can the air be both dry and damp in winter?
Yes. Some rooms, like the living room, can be dry while bathrooms and bedrooms become damp. Measure in several rooms with a hygrometer to see where you need to raise or lower the moisture.
