Waking up to foggy windows outside on a clear morning doesn't mean they're leaking

Glass loses heat by radiating it upward, and on a clear night with little wind, that heat escapes straight into the sky instead of staying trapped under cloud cover. The glass surface can end up colder than the surrounding air, and once it drops below the dew point, humidity in the air condenses directly onto it — the exact same process that beads dew on a lawn overnight.

It only takes high humidity, calm air, and a clear sky to set it up, which describes a lot of Florida mornings outside the driest winter stretches. The water shows up on the outside of the glass, not trapped between panes, and it's gone within an hour or two once the sun warms the surface back above the dew point.

It's easy to mistake for a sign of a bad window or a cleaning job that didn't hold, but it's really just outdoor dew forming on the coldest flat surface around — and good, well-sealed windows do it just as readily as older ones.