Why is there condensation on the outside of my windows in the morning?

Exterior window condensation in the morning is actually a good sign - it means your windows are energy efficient and properly insulating your home from outdoor temperature changes.

This condensation forms when your window glass surface is cooler than the outdoor air temperature and humidity level. During Ottawa's cool mornings, especially in spring and fall, the outdoor air contains moisture that condenses into water droplets when it contacts your cooler window surface. It's the same process that creates dew on grass - the glass acts like a cold surface that moisture in the air clings to.

Modern energy-efficient windows actually promote this exterior condensation because they're doing their job of keeping indoor heat inside rather than transferring it through the glass. Older, less efficient windows would warm up from indoor heat transfer, preventing this natural condensation process. So if you're seeing morning dew on the outside of your windows, your windows are likely performing well thermally.

In Ottawa's climate, this is particularly common during shoulder seasons when overnight temperatures drop significantly but daytime humidity remains higher. The condensation typically disappears as the sun rises and warms the glass surface, or as outdoor humidity levels change throughout the day.

The key difference from problematic condensation is location - exterior condensation is normal and harmless, while interior condensation between glass panes indicates seal failure, and excessive interior condensation suggests humidity control issues. If you're seeing condensation on the inside surface of your windows or between glass panes, that would warrant attention from a window professional.

If you have questions about how your own windows are performing, request a free quote through Ottawa Window Pros — an installer can look at them and talk through any condensation or thermal concerns.