The National Fenestration Rating Council (NFRC) explained the new Condensation Index to the industry last week in a webinar hosted by Dennis Anderson, program manager. He started by telling many of the window manufacturers in attendance what they already know.

When condensation appears the first thing the consumer wants to do is blame the window manufacturer,” said Anderson. “Windows do not create the moisture for condensation, they only react to their environment.”

He then gave a summary of existing condensation ratings and their test methods.

  • NFRC 500-2017, Procedure for Determining Fenestration Product Condensation Resistance Values. The rating achieved is Condensation Resistance.
  • ANSI/NFRC 500-2020, Procedure for Determining Fenestration Product Condensation Index Values. The rating achieved is Condensation Index (CI).
  • CSA (Canadian Standards Association) A440.2-14/A440.3-14, Fenestration energy performance/User Guide to CSA A440.2-14, Fenestration energy performance. The optional condensation rating within this method is titled the Temperature Index (I).
  • FGIA (Fenestration & Glazing Industry Alliance, formerly the American Architectural Manufacturers Association and Insulating Glass Manufacturers Alliance) –AAMA 1503-09, Voluntary Test Method for Thermal Transmittance and Condensation Resistance of Windows, Doors and Glazed Wall Sections. The condensation portion of this test method determines a Condensation Resistance Factor (CRF).

The new NFRC CI simulation method was based on CSA/A440.2/A440.3 for its predication capabilities, said Anderson.

“For a particular application (i.e., for a given winter outside design temperature and indoor relative humidity), the I can be used as a guide for selecting a suitable fenestration system,” he said.

He went on to explain that the I is determined by the placement of sensors along pre-determined locations (and four roving) on the frame/sash and glass. The I value of the product is determined by using the coldest temperature found on the framing or the average of three glass sensors placed 50 mm from the sightline.

The CSA Task Group has agreed to propose a revision to the standard for a simulation method to determine an I value by referencing the ANSI/NFRC 500 procedure,” said Anderson.

The CI will be calculated by user, and software tools to be used for simulation are WINDOW and THERM from Lawrence Berkeley National Lab.

We are on the cusp of introducing software that will calculate all this automatically,” he added.

To sum up the new rating, Anderson explained that as outdoor temperatures get colder, a higher CI is needed. He gave attendees various examples of how windows in certain climates can help limit the likelihood of condensation.

One question from the online audience was whether or not this wil l require a change in the simulation report, to which the answer is yes.

We are moving from CR to CI [on the report],” he said.

For more information, contact the NFCR at

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