I recently attended an educational seminar held at architectural firm in southern Ohio where the topic was condensation resistance of fenestration systems. The interest level for this topic was very high especially since the firm is sometimes working on a project involving schools or hospitals. “Condensation breeds mold, and building owners want to worry less about potential liability associated with subjecting occupants to any sort of conditions which may be detrimental to health,” noted one architect.

Most of the group was very familiar with the concept of U value, how it is determined and what it means when it comes to comparing the thermal insulation performance of various window systems. But when it came to the concept of condensation resistance (CR), I could see that new ground was being broken. After all, CR is a dimensionless unit that is talked about but not always reported and compared for various window systems. When it comes to measuring product attributes, architects typically like to be able to sink their teeth into units. To compound matters, AAMA uses a different method of evaluating CR than does NFRC, so there is no correlation between these two ratings as well. However, looking the bright side, at least we have two widely respected window rating systems with some method of evaluating and comparing the relative ability of various window systems to inhibit the formation of condensation given a standard set of indoor and outdoor conditions.

Why is this important? Because condensation leads to unsightly water buildup on the window and it can drip below to surrounding surfaces causing water damage and subsequent mold growth. So it is an important factor to consider since it can lead to remediation expense and health concerns.

When it comes to NFRC labels, the condensation resistance rating is currently an optional rating and manufacturers may or may not choose to list this on their label. It is expressed as a number from 1 to 100 and the higher the number the better. The AMMA values, called Condensation Resistance Factor (CRF), run between 30- 80, again with higher numbers being better. “At least they have the higher being better thing in common,” remarked one architect or “it might get really confusing!”

The most surprising part of the meeting came when the presenter showed a slide displaying U values of various fenestration products along with condensation resistance factors of the same window systems and there was absolutely no correlation whatsoever between two! Moreover, what shocked many of the architects in the room was that in some cases, the window designs that exhibited the best (lowest) u-values also had the lowest resistances to condensation!

Judging from body language among the group, there were more than a few of those present that were surprised by this. Given the plethora of new low-E coatings coming out every year and the numerous new window designs that are being looked at to get us to R5 (U=.20) and beyond, and given the fact that condensation resistance for these new designs could end being either extremely good or extremely poor, it seems like the whole concept of condensation resistance is something that our industry should definitely keep under a magnifying glass!


  1. AAMA’s online Condensation Resistance Factor (CRF) Tool is intended to provide general guidance on suggesting a minimum CRF based on a project-specific set of environmental conditions. This tool can be found on the AAMA website at http://www.aamanet.org/CRFtool.

    While not an absolute value, the CRF is a rating number obtained under specified test conditions to allow a relative comparison of the condensation performance of the product. It will provide a comparative rating of similar products of the same configuration and permit the determination of the conditions beyond which an objectionable amount of condensation may occur.

    Please feel free to share this tool with anyone interested in condensation resistance. Hopefully, this will serve as a valuable tool to those who are a bit confused by the complexities of condensation.

    Angela Dickson, AAMA Marketing Manager

  2. The wording might lead a person to believe that the AAMA condensation rating factor came after in the NFRC condensation resistance rating. The AAMA CRF has been in place and used extensively for more than 30 years. One of the primary differences between the two methods is that AAMA condensation resistance factor is based on an actual test, whereas the NFRC condensation resistance rating relies on the prediction of a two-dimensional heat flow computer model.

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