Window Ratings And The Climate Factor

We’ve discussed in previous blogs that windows have ratings and that they are also rated for specific climate zones. But how is each climate zone determined? Who comes up with these ratings and why are they important? San Diego homeowners looking to replace their windows need to keep in mind that the consistent amount of sunlight the area receives definitely plays a role in identifying which windows are best suited for their homes. The NFRC LabelFirst, performance criteria for windows and skylights are based on ratings certified by the National Fenestration Rating Council (NFRC).

The NFRC is a non-profit organization that developed and administers a national uniform rating and labeling system for the energy performance of fenestration products (doors, windows, skylights and attachment products). Their main goal is to provide accurate, fair, dependable information to the public on the energy performance of doors, windows, and skylights. When a product has the NFRC label on it, rest assured that it will perform the way it is advertised to perform.

All ENERGY STAR-qualified windows will have an NFRC label that provides its energy performance ratings broken down into four categories; U-Factor, Solar Heat Gain Coefficient (SHGC), Visible Transmittance (VT) and Air Leakage (AL).

U-factor measures the heat from inside your home that can escape, the lower the number the lower chance of wasted heating expenses. Solar Heat Gain Coefficient measures the amount of outdoor heat that can enter your home, the lower the number the lower chance of wasted cooling expenses. Visible Transmittance simply measures the amount of natural light that enters your home, higher numbers mean more outdoor light. Air Leakage simply measures how much air will enter your home through a product, the lower the number the lower potential for draft. For more information, please visit


ENERGY STAR is the trusted, government-backed symbol for energy efficiency. Developed by the U.S. Department of Energy (DOE) and the Environmental Protection Agency (EPA), The ENERGY STAR label was established to reduce greenhouse emissions and other pollutants caused by the inefficient use of energy and to make it easy for consumers to identify and purchase energy-efficient products like replacement windows that offer savings on energy bills without sacrificing performance, features, and comfort (

To achieve a full ENERGY STAR rating, a window must be manufactured by an ENERGY STAR partner, be independently tested and certified by NFRC, and have NFRC ratings that meet strict energy efficiency guidelines as set by the U.S. Department of Energy (D.O.E.)

The Climate Map

Windows that have the ENERGY STAR designation are labeled for specific climatic zones that they are qualified for. Below is a map of the designated climate zones as well as the requirements (U-factor and SHGC) for each of those zones as they pertain to both windows and skylights:

The San Diego Choice

San Diego has been designated as a member of the “South-Central” climate zone and therefore, in order for windows to qualify for the ENERGY STAR label, they must have a U-Factor (rate of heat transfer) of less than or equal to 0.35 and an SHGC (solar heat gain coefficient) of less than or equal to 0.30. Skylights must have a U-Factor of less than or equal to 0.57 and a SHGC of less than or equal to 0.30.

Energy efficiency has come to the forefront of the minds of not only homeowners but manufacturers as well and windows are now being constructed with this as a top priority. US Window & Door is well aware of this and carries only the finest products that are made to not only meet but exceed federal guidelines for energy efficient. Replacement windows that are made by companies like Milgard represent not only the finest in materials and workmanship but also the latest advancements in the world of energy efficiency.