WINDOWS 101

Energy Star

The Department of Energy and the Environmental Protection Agency have developed a program that designates products as ENERGY STAR if they meet certain performance criteria. Since energy-efficient performance of windows and doors varies by climate, Energy Star recommendations are given for four U.S. climate zones. For example, in a heating dominated region, where it gets extremely cold but not extremely hot, you will want to control heat from escaping out, but also allow solar heat and visible light to enter. In other words, you will want to have a window with a very low U-factor, and a high SHGC and VT. Other regions would require different criteria. Figure 2 shows the ENERGY STAR zones and requirements for windows, doors and skylights.


Figure 2


Figure 2 shows California to be in the South/Central Zone. This zone is characterized by both heating and cooling, as opposed to being a strictly heating or strictly cooling dominant zone. This means that both the U-factor, and SHGC, needs to be low in order for the window to perform efficiently. In other words, you want a low U-Factor to block heat from escaping out in the winter, and a low SHGC to block solar heat from entering in the summer. The recommended U-Factor for this zone according to ENERGY STAR should be less than or equal to 0.41. The recommended SHGC for this zone should be less than or equal to 0.36.

The numbers recommended by ENERGY STAR are maximum numbers, and the window purchased will have a SHGC and U-Factor lower than or equal to these numbers. Since these numbers are maximums, there are still lots of variation amongst different windows who fit the ENERGY STAR criteria. This is where the consumer must do their homework. The ideal window for this zone, with respect to energy efficiency, will have very low U-Factor and SHGC ratings, while having a high VT for maximum light. A knowledgeable window and door professional can help you select products that are fit for your region and your criteria.

A window purchasing decision needs to be based on several criteria, such as style, energy efficiency, durability, and cost. So far we have tackled energy efficiency. The following section will discuss the durability of windows and doors.