Why is there ice forming on the inside of my windows even though they're only 5 years old?

Interior ice formation on 5-year-old windows typically indicates excessive indoor humidity combined with poor air circulation, rather than a window defect. Even quality windows can develop ice when indoor conditions create the perfect storm for condensation.

High indoor humidity is the primary culprit behind interior window ice. During Ottawa's harsh winters, when outdoor temperatures drop well below freezing, the interior glass surface becomes extremely cold. If your home's humidity levels exceed 30-40% during winter months, that excess moisture in the air will condense on the coldest surfaces - your windows. This condensation then freezes into ice formations, especially on north-facing windows or those in poorly heated areas.

Poor air circulation around your windows compounds the problem. Heavy curtains, blinds positioned too close to the glass, or furniture blocking airflow prevents warm indoor air from reaching the window surface. Without adequate air movement, the glass stays colder and ice formation becomes more likely. Additionally, if your windows are in rooms with high moisture sources like bathrooms, kitchens, or basements without proper ventilation, localized humidity spikes can cause ice even when other windows remain clear.

In Ottawa's climate, where winter temperatures regularly hit -20°C or lower, even double-pane windows can struggle with interior ice if humidity isn't controlled. The temperature difference between your heated home (around 20°C) and the outdoor air creates a significant thermal bridge through the glass. If your 5-year-old windows are double-pane rather than triple-pane, they're more susceptible to this issue during extreme cold snaps.

To resolve this issue, start by reducing indoor humidity using exhaust fans, dehumidifiers, or improving ventilation. Ensure curtains and blinds allow air circulation around windows, and consider upgrading to triple-pane windows if the problem persists. A professional assessment can determine if your windows need better weatherstripping or if humidity control is the real solution.

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