Philadelphia area ENERGY STAR windows

While the Delaware Valley area doesn't get quite as cold as Minnesota during the winter, it does get much hotter during the summer. ENERGY STAR windows in our region actually have to work efficiently under both conditions of summer heat and winter cold in order to obtain their ENERGY STAR rating.

U-value is a key term to understand when shopping for windows. Simply put, U-value is the mathematical expression for how much heat is lost or gained through four factors:

• conduction
• convection
• radiation
• air leakage

The lower the U-value of a window, the higher the insulating value which is why energy efficient windows and doors have such a low U-value. ENERGY STAR replacement windows will certainly have low U-values to earn the ES rating. But, there are other factors which are also part of the equation.

ENERGY STAR replacement windows factors

Another significant factor to consider when selecting the best replacement windows for your region is the solar heat gain coefficient (SHGC). This factor expresses the length of the sun's rays which are allowed in to your home through the windows.

In extremely hot, sunny places (like Palm Springs, CA), a lower SHGC is a good thing to keep heat generated by the sun out of your home. However, a low SHGC rating would not qualify as ENERGY STAR replacement windows in a colder climate because these windows would not take advantage of warming solar waves during the winter.

Swing climates, like what is present in the Delaware Valley where winters are cold and summers are hot, should have SHGC factors which run between 0.40 and 0.55 to balance out the extremes. ENERGY STAR windows for our area will display the SHGC factor, and you can select options which run from the lower to higher ends of this acceptable range. The lower range SHGC is great for people who feel more uncomfortable in summer heat than in winter cold, and vice versa.