We don’t want to bore you with technical terms like vapour pressure differential. Let’s keep this simple.
There are two rules at work here:
- When warm moist air touches something cool, condensation will form.
- Warm air can hold a lot of moisture; cold air cannot. (While warm air can hold a lot of moisture, it doesn’t necessarily have to. Take a trip to Arizona).
Despite the threats of global warming, it’s still pretty cold outside in the winter. Consequently, windows are cold. If the inner glass surface is extremely cold, condensation (in the form of water or ice) will form, even in a house which has normal indoor humidity. This, believe it or not, is the principle reason for storm windows. The exterior pane of glass provides enough of a buffer zone, that the surface temperature of the interior pane of glass stays warm enough, and condensation is less likely to form.
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