Windows play a key role in high performance buildings, not just in terms of overall energy balance but also considering comfort and health. Energy balance refers to the differences between energy gains and energy losses for any given climate and window orientation, whereas comfort pertains to the difference between interior surface glass temperature and room temperature and health focuses on risk of condensation and mold. All three factors are crucial for ensuring sustainable, comfortable and healthy buildings.
There are currently three difference window rating systems available in North America, namely NFRC (National Fenestration Rating Council), PHI (Passive House Institute) and PHIUS (Passive House Institute US). Bronwyn Barry of One Sky Homes in California explains in the download the differences between the three rating systems, highlighting that the PHI method is the only one which has minimum U-value required for specific climates and minimum performance in relation to condensation risk.