As cooler mornings return to Schomberg, you may notice water on the inside of a window after turning on the heat. The furnace is not necessarily the cause. Warm indoor air holds moisture, and that moisture can condense when it meets cold glass. The useful first step is to find out where the water is and how humid the room is.
Where is the moisture?
- On the room side of the glass: indoor moisture is meeting a cool surface. Check humidity, ventilation and airflow around the window.
- Between sealed panes: Natural Resources Canada notes this can indicate a failed seal in the insulating glass unit. A window professional can assess it.
- On the wall, trim or sill: dry the area and investigate promptly. A leak or ongoing condensation can damage materials.
Measure humidity before changing settings
A small hygrometer can show the relative humidity in the room. Check it at different times, especially after cooking or showering. Health Canada recommends keeping indoor relative humidity between 30% and 50% to help control moisture and mould. On very cold days, condensation may still appear on a cold window within that range; the right level depends on the window and the weather. Avoid turning a humidifier up simply because the heating season has started.
Five safe steps to try
- Use the bathroom exhaust fan during showers and for at least 30 minutes afterward, as Health Canada advises.
- Run the kitchen exhaust fan when cooking, and check that it vents outdoors.
- Let warm room air reach the glass. Open heavy curtains or blinds when practical, and keep furniture away from heating vents or baseboards.
- Dry wet sills and frames. Standing water can wet trim and surrounding materials.
- Check any humidifier setting. If you have a whole-home humidifier and the windows stay wet, note the humidity reading and ask a qualified HVAC technician to check its operation. Leave internal equipment, wiring and gas components to a professional.
When is it time to call someone?
If moisture keeps returning, paint is peeling, or you see or smell mould, address the moisture source rather than just wiping the glass. A window or building professional may be needed for leaks, cold surfaces or failed sealed units. If the concern involves your home’s humidifier, ventilation or heating airflow, see our heating and cooling services or call Schomberg Heating & Cooling at (905) 939-2350. Please call instead of relying on the website form while its email delivery is being checked.
Sources: Health Canada: Guide to addressing moisture and mould indoors; Natural Resources Canada: Condensation.