Selecting Window Glass: ENERGY STAR Climate Zones in the USA


ENERGY STAR is a good tool to help narrow down your options so you can select the window glass package that best fits your needs. As you might expect, different combinations of window features are more beneficial in different climates. In the US, four climate zones have been identified based on the amount of sun, heat and cold they receive throughout the year. In general, the further North you live, insulation value (U-Factor) is more important. As you move South, reflecting heat from the sun (SHGC) becomes more important.

Understanding Glass Performance

U-Factor – measures how well the window prevents heat from entering or escaping the home. Ratings generally fall between 0.2 and 1.25. Windows with a lower U-Factor provide better insulation. U-Factor is important wherever you live, but is a primary concern for homes in colder Northern climates.

Solar Heat Gain Coefficient (SHGC) – measures how much heat from the sun is blocked. This number can range from 0 to 1 where windows with lower numbers reflect more heat. This is particularly important during the summer in hot Southern climates.

Visible Transmittance (VT) – measures how much light comes through the whole window. Ranging from 0 to 1, windows with higher numbers allow more light into the home.

Air Leakage – measures how much outside air comes into the home through a closed window. Rates typically fall in a range between 0.1 and 0.3*. The lower the air leakage number, the lower the potential for draft through the window.

Condensation Resistance (CR) – measures how well the window resists the formation of condensation on the inside of the window. CR is expressed as a number between 1 and 100. The higher the number, the better the window is able to resist condensation.

Energy Rating (ER- Canada Only) – measures the overall energy performance of a window. The Energy Rating is based on the combination of Air Leakage, U-Factor and Solar Heat Gain. The higher the ER number, the better the product’s overall energy performance

2016 ENERGY STAR Criteria
  U-Factor SGHC  
Northern Zone ≤ .27 Any Prescriptive*
= .28 ≥ .32 Equivalent
= .29 ≥ .37
= .30 ≥ .42
North-Central Zone ≤ .30 ≤ .40
South-Central Zone ≤ .30 ≤ .25
Southern Zone ≤ .40 ≤ .25

Air Leakage ≤ 0.3
*ENERGY STAR 2015 Criteria for the Northern Zone: U-Factor ≤ .30, SHGC = Any Criteria for all other zones are the same for 2015.

Cutting-Edge Energy Efficiency

With the ENERGY STAR Most Efficient designation, products are recognized as the latest in technology innovation for cutting-edge performance. Latitude Glass options that meet these stringent criteria are available for all zones and offer different levels of view clarity. If you desire the best performance, choose windows that meet ENERGY STAR Most Efficient criteria.

Most Efficient Criteria

  U-Factor SGHC
Northern ≤ .20 ≥ .20
North-Central ≤ .20 ≤ .40
South-Central ≤ .20 ≤ .25
Southern ≤ .20 ≤ .25

Air Leakage ≤ 0.3

The Best Value for You

Choosing the right glass for where and how you live is the best way for you to get the most from your new windows. As you make this important decision, keep in mind how the windows will look, the amount of light you want coming in to your home and the level of insulation that will make you the most comfortable.