Residential building energy consumption is dependent on many variables. The heat loss or gain attributable to fenestration products can be a significant portion of the whole building load. The fenestration industry is currently developing and implementing new test methods and rating procedures to more accurately account for fenestration energy transfer. One of the tools being developed by the National Fenestration Rating Council (NFRC) is a PC-based program called Residential Fenestration (RESFEN) heating and cooling load use and costs.

This paper will provide a review of the energy and cost impacts that variable air leakage rates of several types of window products can have on overall window energy usage as modeled in four typical building designs located in the United States. The analysis was performed with the RESFEN software as part of an NFRC sensitivity study on this issue.