Winter ventilation in your home: How to get fresh air without cooling

How many minutes to air out an apartment in winter

Experts at the Energy Saving Trust recommend opening windows at least two to three times a day for about five minutes, even in cold weather.

The most effective method is to open windows wide for a short period. If your apartment's layout allows, you can open windows on opposite sides of the home to help air circulate through the rooms more quickly.

This method is known in Germany as Stoßlüften, or intensive ventilation. The principle is simple: instead of leaving a window slightly open for hours, exchange air actively for a few minutes.

However, five minutes is a guideline, not a rule for every apartment. The duration depends on the outdoor temperature, wind speed, room size, and the number of people at home.

During severe frosts, avoid letting rooms get too cold. In unfavorable weather or when outdoor air quality is poor, adjust the ventilation method accordingly.

Why short bursts of ventilation help preserve heat

The main advantage of intensive ventilation is that it allows you to replace a significant portion of indoor air in a short time without substantially cooling the walls, floors, and furniture.

That's because a home stores heat not only in the air but also in building materials and furnishings.

When you open a window for just a few minutes, some warm air escapes, but most surfaces remain relatively warm. Once you close the windows, the room can quickly return to a comfortable temperature.

However, if you leave a window slightly open for several hours, cold air will continuously enter the room. This can cool the walls and window reveals near the opening.

Experts recommend using windows on the sunny side of the building whenever possible, as the air near them may sometimes be warmer than on the shaded side.

However, avoiding heat loss entirely is impossible. The goal of proper ventilation is to ensure an adequate supply of fresh air without unnecessarily cooling the apartment.

When to open windows more often

Ventilating two or three times a day may not be enough if significant amounts of moisture or pollutants accumulate in your apartment.

After sleeping. Carbon dioxide and moisture from breathing can build up in the bedroom, especially if you keep the doors and windows closed all night. Morning ventilation helps refresh the air more quickly.

While cooking. Boiling water, frying food, and using a gas stove can affect indoor air quality. Turn on an extractor hood that vents air outdoors while cooking, or, if you don't have one, ventilate the kitchen.

After a shower or bath. Hot water increases humidity, causing steam to settle on mirrors, tiles, and other cold surfaces.

When drying laundry. Moisture from freshly washed clothes evaporates into the air. If the room is poorly ventilated, this can contribute to condensation.

After using household cleaning products. Some cleaning products release substances that can reduce indoor air quality. Follow the instructions on the packaging and ensure adequate ventilation.

Energy Saving Trust experts recommend leaving an extractor fan in the bathroom or kitchen running for about 15 minutes after showering or cooking.

Why you should avoid blocking vent openings in winter

Some people seal ventilation grilles or close small vents in window frames to keep cold air out. However, this can reduce ventilation and contribute to moisture buildup.

Small ventilation openings installed in modern windows are designed to provide a controlled supply of fresh air. Energy Saving Trust experts generally recommend keeping them open even in winter.

These vents should not be confused with a regular open window. They allow smaller amounts of air to enter and are part of the ventilation system.

It is especially important not to block ventilation in rooms with gas appliances. An insufficient air supply can create dangerous operating conditions for these appliances.

If your apartment has a mechanical ventilation system, follow the manufacturer's recommendations. In such homes, the need to open windows may differ.

What to do if windows still fog up after ventilation

Condensation forms when moist air meets a cold surface. In winter, this is most commonly noticeable on glass, window frames, and reveals.

A small amount of moisture after showering or in the morning does not always indicate a serious problem. However, if water regularly collects on the windowsill or dark spots appear on the walls, you should check humidity levels and ventilation performance.

According to recommendations from the US Environmental Protection Agency (EPA), indoor relative humidity should ideally be maintained between 30% and 50%. To reduce the risk of mold growth, it should not remain above 60% for extended periods.

You can monitor this level using a hygrometer, a small device that measures air humidity.

If water keeps appearing on your windows, try the following:

• Check whether ventilation grilles and air inlets are blocked.

• Turn on the extractor hood regularly while cooking and after showering.

• Avoid drying large amounts of laundry indoors without adequate air circulation.

• Wipe condensation off window frames and windowsills to prevent water from accumulating.

• Check whether any rooms are remaining excessively cold.

If the problem persists, possible causes include insufficient insulation, cold spots on walls, faulty windows, or ventilation problems.

A dehumidifier can sometimes help reduce humidity, but it does not replace ventilation because it does not provide a supply of fresh air.

Common ventilation mistakes to avoid

Leaving a window slightly open for hours. In cold weather, this can cause surfaces near the window to cool down over an extended period. Short, intensive ventilation is often more effective for quickly refreshing indoor air.

Completely avoiding fresh air. Even if an apartment is well insulated, it still needs proper air exchange. An airtight home without adequate ventilation can contribute to moisture and pollutant buildup.

Blocking ventilation to keep the heat in. Sealed grilles and closed air inlets can reduce air quality and, in some cases, create safety risks.

Ignoring musty smells. If the smell returns quickly after ventilation, investigate possible moisture sources rather than simply opening windows more often.

Ignoring your apartment's specific features. General advice may need adjustment for homes with mechanical ventilation, gas appliances, or insulation problems.

The best approach in winter is to combine regular short bursts of ventilation with a properly functioning ventilation system and humidity monitoring. This helps maintain a comfortable indoor environment without losing unnecessary heat.