Do you need a dehumidifier in winter?

You may need a dehumidifier even in winter, especially in garages, basements, crawl spaces and other cold areas. But the need is not the same everywhere. During prolonged cold spells, outdoor air often contains little water vapour, while milder weather, melting snow and moisture from the house can cause problems. Whether dehumidification is necessary depends on the moisture conditions in your particular space.

When do you need a dehumidifier in winter?

Winter moisture problems often arise when warm air meets a cold surface. If the surface is colder than the air's dew point condensation can form. You may notice misted-up windows or damp patches on cold walls, but in crawl spaces and attics it can happen out of sight.

Moisture is also added inside a heated home through showering, cooking and doing laundry. Proper ventilation is usually the first step there. In a cold garage, storage room or crawl space, however, dehumidification may be needed if the moisture cannot escape through ventilation or dry out.

Where you live makes a difference

During extended cold spells in northern Sweden, outdoor air often contains little water vapour. When that air is heated, its relative humidity falls, which helps explain why indoor air can feel dry in winter.

In southern Sweden and coastal areas, winters are often milder, with more periods of humid outdoor air and rapid temperature changes. If damp air enters a space that is still cold, its relative humidity may rise and condensation may form. The same can happen in the north during a thaw.

Does the dehumidifier need to run when it is very cold?

In a crawl space, moisture entering from outdoor air often decreases during a cold winter, but moisture can still come from the ground or through leaks. The need for dehumidification also often increases in spring and summer when warmer outdoor air cools inside the cold crawl space. Read more about moisture from outdoor air in crawl spaces.

If you already have a demand-controlled dehumidifier, it is generally better to let its controls determine when dehumidification is needed than to turn it off simply because it is winter. Dehumidification itself may pause when conditions allow, but the fan may continue running depending on the model and settings. Always follow the operating instructions.

Which spaces may need dehumidification in winter?

• Basements: Cold external walls and floors may develop condensation if the air is humid enough. Also check whether moisture is entering through the building structure.
• Garages: A snow-covered car brings in water that collects on the floor and then evaporates. This can cause condensation and rust on tools and other metal parts. Read more about dehumidifiers for garages.
• Crawl spaces and cold attics: Moisture loads are often greater during other seasons, but air leaking from the home, ground moisture and changes in weather can cause problems in winter too.
• Storage rooms and other unheated spaces: Damp belongings, air leaks and poor air circulation can leave cardboard boxes, textiles and other materials feeling clammy or developing an unpleasant smell.

When is a dehumidifier usually unnecessary?

If a heated room has adequate ventilation and there are no signs of moisture problems, there is normally no reason to install a dehumidifier. The same applies to a dry storage room where measurements over time show acceptable conditions. Air that is too dry indoors can also be uncomfortable, particularly during cold winter weeks.

How to tell whether you need dehumidification

Start by finding out where the moisture is coming from. A dehumidifier can reduce humidity, but it cannot stop roof leaks, water ingress or other damage to the building.

1. Measure temperature and humidity. Track the readings with a hygrometer during both cold spells and milder weather. A single reading rarely tells the whole story.
2. Look for condensation and damp surfaces. Check windows, cold corners, pipes, walls and materials stored close to external walls.
3. Pay attention to odours and visible damage. Recurring musty smells, discolouration or damp building materials should be investigated, even if the hygrometer shows moderate readings.
4. Identify the cause before choosing a solution. Ventilation, drainage, repairs and dehumidification serve different purposes. In a crawl space, any changes to ventilation or sealing must be assessed for that particular construction.

There is no single relative humidity threshold at which mould will always start growing. The risk also depends on temperature, materials and how long the moisture remains. Repeated condensation or persistently high humidity is a reason to investigate conditions more closely.

How to use a dehumidifier efficiently in winter

• Fix unnecessary air leaks. Open doors and gaps can bring in more moisture and increase the amount of work the dehumidifier has to do. However, do not seal vents or ventilation openings without first assessing their purpose.
• Use demand-based control. Our EvoDry RCF 20 G1 and other RCF models can adjust dehumidification according to temperature and relative humidity. This can reduce unnecessary operation when the risk from moisture is lower.
• Maintain good air circulation. The dehumidifier needs to reach the areas that must be kept dry. Adapt its location and any ductwork to the space.
• Choose technology suited to the temperature. Many conventional compressor dehumidifiers lose capacity in cold conditions. A desiccant dehumidifier can operate below freezing if its specified operating range and installation permit it. Read more about dehumidifiers in sub-zero temperatures.

How do you know if your old dehumidifier is sufficient?

Do you already have a dehumidifier that runs a lot but still cannot bring the humidity down? First check the filters, airflow, settings and whether the moisture load has changed. A blocked duct, a new water leak or a poorly positioned sensor can produce the same symptoms as an undersized dehumidifier.

If the dehumidifier is correctly installed and working as intended but still cannot cope with the moisture load, you may need a model with a different capacity or technology. Our desiccant dehumidifiers are one option where temperatures vary considerably, but your choice should be based on the space's volume, moisture sources and other conditions – not just the season.