Glass Glossary

Relative Humidity (RH)

Last Updated: November 23, 2023

Relative humidity (RH) refers to the amount of moisture present in the air, compared to the maximum amount the air can hold at a specific temperature. Expressed as a percentage, it indicates the current humidity level as a fraction of the maximum possible humidity. A higher RH denotes a greater moisture content in the air and a closer proximity to the air’s saturation point.

Relative humidity is crucial in determining the formation of interior condensation on window glass. When warm, moisture-laden air contacts a cooler surface, such as a window pane, it causes the moisture in the air to condense into water droplets. The likelihood of condensation increases as indoor relative humidity rises, particularly when outdoor temperatures drop and the interior window surface cools.

Interior condensation can be detrimental as it obscures visibility, damages window frames, and may lead to mold growth. To minimize condensation, it is important to manage indoor relative humidity levels, which can be done through proper ventilation, the use of dehumidifiers, and by installing energy-efficient windows that lessen temperature differences between the interior window surface and the ambient air.

In particular, insulating glass with LoĒ™ coatings and argon gas fill can significantly reduce condensation on window glass. LoĒ coatings on surface #2 of an insulating glass unit reflect heat escaping the home back into the interior pane of glass, warming it up during the winter. LoĒ coatings on surface #2 with argon gas are an excellent insulator that maintains a higher glass surface temperature, furthering resistance to interior condensation. LoĒ coatings also prevent longwave radiation heat from escaping the home in winter, contributing to more comfortable interior temperatures and reducing condensation risk.