Condensation Resistance and Ratings

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Last Updated: July 30, 2024

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 a number of methods used to measure condensation resistance. In this article, we will outline three: the Condensation Resistance Rating (CR), the Condensation Index (CI), and the Condensation Resistance Factor (CRF). CR and CRF are calculated based on laboratory tests that simulate real-world conditions, while CI is simulation-based, using specific environmental conditions for a predictive measure, and is applicable to diverse climatic conditions.

Condensation Resistance Rating (CR)

Developed by the National Fenestration Rating Council standard NFRC 500-2017, the CR is a number between 0 and 100, with higher values indicating better condensation resistance. It is calculated based on factors such as the temperature of the room-side surface of the window and the relative humidity of the indoor air.

Condensation Index (CI)

Also developed by the NFRC, the ANSI/NFRC 500-2023 CI was made to replace the older CR calculation. The CI for a window is calculated using Berkeley Lab WINDOW and THERM software. It is made to predict, through simulation, a fenestration system’s ability to resist condensation in varied regional weather conditions.

Condensation Resistance Factor (CRF)

Developed by the Fenestration & Glazing Industry Alliance (FGIA, formerly AAMA) standard AAMA 1503-09. 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 room-side surface of the window under specific conditions of temperature and humidity. The laboratory test determines the overall CRF by comparing the relative CRF of the glass and the frame, and choosing the lower of the two values.

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 room-side surface of the glass. The type of LoĒ coating, the gas used, the width of the airspace, the spacer design and material, and the quality of the seals all influence the condensation resistance of an IG unit.

Frame Materials: The materials used for the window frame also affect condensation resistance. High-performance frames provide better insulation than frames with traditional materials and design. This helps to prevent cold spots where condensation is more likely to form.

How Cardinal Glass Improves Overall Condensation Resistance

Cardinal produces LoĒ™ glass coatings and insulating glass (IG) units are designed to reduce the potential of condensation.

Cardinal’s primary LoĒ coatings dramatically lower Center-of-Glass U-factor, keeping wintertime heat inside the room, which also improves the room-side glass surface temperature.
Cardinal’s IG units with a stainless-steel spacer system also contribute to lowering condensation risk. Products like Endur® and XL Edge® are warm edge spacers, meaning their materials and design lower thermal conductance at the edge of glass, an area normally prone to condensation.

In most cases, a Cardinal IG unit with argon fill and a LoĒ coating will provide the greatest condensation resistance of the entire window assembly. This is because the frame and sash materials tend to have a higher U-factor, which effectively lowers the surface temperature of the frame.

Overall, the best solution to beat condensation to use a 2 or 3 pane IG unit with one or more LoĒ coatings and argon fill, installed in an energy-efficient window frame.

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