Will your windows sweat tonight?
Condensation forms when a surface is colder than the air's dew point. Check your numbers before the overnight low hits.
Evidence-checked. Facts and figures on this page are verified against published standards and government sources (Magnus dew-point formula (Sonntag coefficients)). Last verified July 2026 — our methodology.
Verdict
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- Dew point of your air
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- Est. inner glass temp
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- Safety margin
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- RH to stay safe
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Dew point uses the Magnus formula (accurate to ~0.2°F in this range). Inner-glass temperature is an estimate from typical glazing heat-loss factors — real windows vary with frames, curtains, and air circulation. "RH to stay safe" is the indoor humidity at which the dew point drops 3°F below the estimated glass temperature.
If you're at risk
Three levers, in order of cost: run bath and kitchen fans longer to cut indoor moisture at the source, lower indoor RH with aproperly sized dehumidifier, and keep air moving across the glass (open curtains help more than people expect). Persistent condensation between panes means a failed seal — that's a window repair, not a humidity problem.