Glass Glossary

Condensation Resistance

Last Updated: December 19, 2023

Condensation resistance is the ability of a window, door, or skylight to resist the formation of condensation on its room-side surface. This is an important factor in window performance, as excess condensation can lead to mold growth, damage to window frames and sills, and reduced visibility. Condensation typically occurs when warm, moist air meets a colder surface, causing the moisture in the air to condense into water droplets. The propensity for condensation to form is influenced by several factors including the temperature of the surface, the humidity of the indoor air, and the thermal performance of the window.

There are two metrics used to measure condensation resistance: the Condensation Resistance Rating (CR) and the Condensation Resistance Factor (CRF). Both are calculated based on laboratory tests that simulate real-world conditions.

Condensation Resistance Rating (CR)

Developed by the National Fenestration Rating Council (NFRC), the CR is a number between 1 and 100, with higher values indicating better condensation resistance. It is calculated based on factors such as the temperature of the interior surface of the window and the relative humidity of the indoor air. NOTE: This may have to be updated to instead use the (CI) rating:

Condensation Resistance Factor (CRF)

Developed by the Fenestration & Glazing Industry Alliance (FGIA, formerly AAMA). The CRF is a number between 30 and 80, with higher values indicating better condensation resistance. It measures the temperature at which condensation begins to form on the interior surface of the window under specific conditions of temperature and humidity.

Influence of IG and Frame Materials on Condensation

Insulating Glass (IG) Units: IG units are composed of multiple panes of glass separated by a spacer and sealed to create a single unit with an air or gas-filled space in between. This design helps to reduce heat transfer through the window, which in turn lowers the risk of condensation forming on the interior surface of the glass. The type of LoĒ coating, gas used, the width of the airspace, and the quality of the seals all influence the condensation resistance of an IGU.

Frame Materials: The material used for the window frame also affects condensation resistance. High-performance frames made from materials like composites, vinyl, or thermally broken aluminum provide better insulation than traditional materials like untreated aluminum. This helps to prevent cold spots where condensation is more likely to form.

Overall, condensation resistance is influenced by the combination of the IG unit, frame materials, and the quality of the window’s installation. Both CR and CRF can be useful in assessing the condensation resistance of a window, but they are not directly comparable due to differences in their calculation methods and scales. Nonetheless, both metrics can help consumers, architects, and builders select windows that are appropriate for their specific needs and climate conditions.