Window condensation is not really a glass-cleaning problem. You have to change the conditions that put the glass below the dew point: too much indoor moisture, a very cold surface, or both.
Measure indoor humidity first
Use a hygrometer and see whether condensation lines up with high readings. If humidity rises after showers, cooking, or indoor clothes drying, start with source control and exhaust.
Use exhaust fans effectively
A bathroom fan should discharge outdoors. Run it during the shower and for a while afterward. Use outdoor-venting kitchen exhaust when cooking creates heavy steam.
Let room air reach the glass
Avoid sealing windows behind heavy curtains all day in cold weather, and do not block all circulation with furniture. Opening blinds or curtains for part of the day can help warm the interior surface.
Do not confuse ventilation with always opening a window
Brief ventilation can help during cold, dry weather. During humid outdoor conditions, opening windows may add moisture. Use outdoor conditions rather than a fixed rule.
Dry water that has already formed
Wipe droplets from frames and sills. Do not leave wood, seals, paint, or drywall wet day after day while you work on the cause.
When the window itself is part of the problem
Very cold glass, conductive frames, and air leakage can encourage condensation. Appropriate weatherstripping, better glazing, or insulation improvements can raise interior surface temperatures. Do not block designed drainage paths.
Do not raise the thermostat just to dry windows
More heat can raise glass temperature, but it also increases energy use and does not correct excessive indoor moisture. Address showers, cooking, indoor drying, leaks, and exhaust before using whole-house temperature as the main fix.
Compare rooms instead of treating every window the same
If condensation affects only one bedroom, compare door position, occupancy, curtains, and airflow. If it affects nearly every window, the cause is more likely house-wide humidity, very cold weather, or the thermal performance of the windows.
The durable fix changes humidity and surface temperature instead of only wiping the glass every morning.
Sources
- U.S. Environmental Protection Agency (EPA) — Indoor Air Quality — Indoor humidity, ventilation, particles, and indoor air quality.
- U.S. Environmental Protection Agency (EPA) — A Brief Guide to Mold, Moisture and Your Home — Moisture control, drying, and general household mold guidance.