Glass Glossary

Indoor Condensation


Last Updated: November 23, 2023

Maintaining a Desirable Humidity Level

People are most comfortable when relative humidity ranges between 20% and 60%. In the home, an average relative humidity of 35% to 40% is appropriate when the outside temperature is 20 °F (-7 °C) or above. However, during cold weather, higher humidity ranges may cause indoor condensation on windows.

The table below shows recommended indoor humidity levels in relation to outdoor temperatures.

Outdoor Temperature °F Recommended Relative Humidity
20° and Above
35% to 40%
+10°
30%
25%
-10°
20%
-20°
15%

Figure: Recommended indoor humidity levels

The table below shows the relationship of condensation to indoor glass and room relative humidity. If glass conditions are above the line in the chart, expect to see condensation. If they are below the line, you won’t see condensation.

Relative Humidity (%)

Figure: % relative humidity vs indoor glass surface temperature