Why Is There Condensation on the Inside of My Windows in Winter?

 

Condensation on apartment window

You wake up on a cold morning and find water droplets along the bottom of your window. Sometimes the glass is completely fogged up. You wipe it dry, but the moisture returns the next day.

This happens when warm indoor air meets a cold window surface. The air near the glass cools, and some of its moisture turns into water droplets. It is especially common in winter, when the difference between indoor and outdoor temperatures is large.

A little fog that disappears quickly may be manageable. Water that repeatedly collects on the sill or soaks into the frame needs attention. The useful question is not simply “How do I wipe it away?” but “Where is the moisture coming from, and why is this window staying wet?”

First, check where the moisture is

The location of the water gives you an important clue.

On the room-facing surface of the glass: This is usually indoor condensation. You can reach it with a cloth, and it often appears overnight or after cooking, showering, or drying laundry.

On the outside surface: Exterior condensation can happen under certain weather conditions. It does not necessarily mean moisture is building up inside your apartment.

Between two panes of glass: If you cannot wipe the fog away from either side, the sealed window unit may have a problem. Reducing indoor humidity will not remove moisture trapped between panes; ask building maintenance or a window professional to inspect it.

This article focuses on water forming on the inside surface of a window.

Why does it happen more often in winter?

Indoor air contains moisture from everyday activities. Cooking, showering, breathing, and drying clothes all add water vapor to the air. A cold window gives that moisture a place to condense.

That is why the same apartment can have dry-looking windows in one season and wet windows in another. It also explains why one window may be worse than the rest: it might be colder, receive less warm airflow, or sit behind a closed curtain.

Condensation is a clue, not a complete diagnosis. The room’s humidity matters, but so do the temperature of the glass, ventilation, and the way air moves around the window.

How to reduce condensation on your windows

1. Dry the glass, sill, and frame

Start with the water you can see. Wipe the glass and the bottom edge of the frame, then check the corners and the surface below the sill. A cloth left soaking on the windowsill only keeps that area damp, so remove it when you finish.

Do this promptly whenever water appears. The U.S. Environmental Protection Agency advises drying condensation on windows and reducing its moisture source because persistent moisture can encourage mold growth.

2. Use kitchen and bathroom exhaust fans

Cooking and showering can send moisture through a small apartment. Use an exhaust fan that actually vents outdoors when those activities produce steam. Keep it running long enough to clear the damp air, and check that the vent is working.

If your apartment has no effective exhaust fan, ventilation may help when outdoor conditions and safety permit. The goal is to let moist air leave rather than allowing it to settle on cold surfaces.

3. Watch what happens when you dry laundry indoors

An indoor drying rack releases moisture as clothes dry. If your windows are wet on laundry days but relatively dry on other days, that is a useful clue.

Spread clothes out, avoid crowding the rack, and ventilate the space or use a dehumidifier if needed. For a detailed drying routine, see How to Dry Clothes Indoors in a Small Apartment Without Musty Smells.

4. Check the humidity before adding more moisture

A small hygrometer can show whether your apartment stays humid, especially overnight. If you use a humidifier, check its setting rather than assuming the room needs more moisture.

There is no single humidity number that guarantees dry windows in every home. A colder window can collect water even when the rest of the room feels comfortable. If condensation increases after you run a humidifier, lower its output and watch what happens over the next few mornings.

For a broader guide, see How to Keep Your Apartment at the Right Humidity in Winter.

5. Let room air reach the glass

A curtain pressed tightly against a window can leave the space behind it cooler and less ventilated. In the morning, open the curtain and check whether the glass and sill are damp. Move furniture or other items that block normal airflow around the window.

This does not mean you must leave curtains open all night. It means checking whether moisture is being trapped where you cannot see it. For the heating and privacy trade-offs, see Should You Keep Curtains Open or Closed in Winter?

6. Look for a window or building problem

If one window is consistently much wetter than the others, examine the frame and nearby wall. Check for damaged seals, visible gaps, staining, peeling paint, or a damp patch that remains even when you reduce indoor moisture.

Report recurring water damage to your landlord or building manager. Moisture from a leak or a window defect calls for a different fix from ordinary surface condensation.

Should you use a dehumidifier in winter?

A dehumidifier may help if your apartment has a persistent moisture problem, especially when you frequently dry clothes indoors. But it is not automatically the first thing to buy.

Try identifying the moisture source, using working exhaust fans, and measuring humidity first. If the room is already dry while one window stays wet, the window’s cold surface or limited airflow may be the more useful place to investigate.

If you do use a dehumidifier, follow its instructions, empty and clean it as directed, and check whether the windows actually improve. The goal is a drier window and a comfortable room, not the lowest possible humidity reading.

What if you see mold around the window?

Do not ignore repeated dark patches on a damp sill, seal, or nearby wall. Cleaning a visible patch without fixing the moisture problem may leave you dealing with it again.

The appropriate cleanup depends on the material, the extent of the growth, and whether water has reached hidden areas. If the affected area is extensive, keeps returning, or appears alongside a leak or damaged wall, contact your landlord or a qualified professional. The CDC notes that mold grows where moisture is present, including around leaking windows, and emphasizes addressing the water problem.

A simple check for the next three mornings

Checking humidity near a window

If you are unsure what is causing the condensation, make a short record:

1. Check the windows when you wake up. Note which ones are wet and whether water has reached the frame.
2. Record what happened the evening before. Did you cook, shower, dry laundry, or run a humidifier?
3. Check the room’s humidity reading, if you have a hygrometer.
4. Change one practical thing at a time. For example, use the bathroom exhaust fan consistently, then compare the next few mornings.

You do not need a perfect experiment. A few observations can show whether moisture-heavy activities are driving the problem or whether one window needs closer inspection.

Frequently Asked Questions

Is condensation inside a window normal in winter?

It is common for moisture to form on a cold interior window surface. What matters is how much water collects, how often it returns, and whether the frame or wall stays damp.

Why is only my bedroom window wet?

That window may be colder or receive less airflow. A closed curtain, overnight moisture, or differences in the window itself may also play a part. Compare it with other windows and check for signs of damage.

Will wiping the window solve the problem?

Wiping prevents water from sitting on the frame and sill, so it is a useful first step. If condensation returns each morning, you also need to address the moisture source, airflow, or window condition.

Does condensation between window panes mean my apartment is too humid?

Not necessarily. Fog trapped between panes can indicate a problem with the sealed glass unit. Have the window inspected if you cannot wipe the moisture from either exposed surface.

Final Thoughts

Start by drying the window and finding out when and where the water appears. Then reduce moisture from daily activities, make sure ventilation works, and check whether warm room air can reach the glass. If water keeps returning to the same window or damages the surrounding surface, have the window and nearby wall inspected.