Any window worth their salt would be certified by ENERGY STAR.
ENERGY STAR is a voluntary energy efficiency program established by the U.S. that promotes energy-efficient products and practices by certifying products that meet strict energy efficiency guidelines.
The ENERGY STAR label, found on windows from an ENERGY STAR partner, signifies their energy efficiency. Here’s an example of an ENERGY STAR label:
The ins and outs of an ENERGY STAR label
In order for a window to be ENERGY CERTIFIED, a list of requirements must be achieved within acceptable energy performance ratings. Here are the performance ratings that need to be achieved (they will also be listed on the label itself):
U-factor
This measures how well the window insulates. A lower U-factor indicates better insulation, meaning less heat transfer between the interior and exterior of the building.
Solar Heat Gain Coefficient (SHGC)
This measures how much solar heat is transmitted through the window. A lower SHGC indicates that the window blocks more solar heat, which can help reduce cooling costs in warm climates.
Visible Transmittance (VT)
This measures how much visible light passes through the window. A higher VT means more natural light enters the building, reducing the need for artificial lighting during the day.
Air Leakage (AL)
This measures how much air passes through the window assembly. ENERGY STAR-certified windows typically have lower air leakage rates, which helps improve energy efficiency by reducing drafts.
Condensation Resistance
This measures how well the window resists condensation forming on its surface. Higher condensation resistance ratings indicate that the window is less likely to experience condensation, which can help prevent moisture-related issues like mold and mildew.
Now that we’ve familiarized ourselves with the ENERGY STAR label, it is important to note that there isn’t a perfect rating per se.
Different windows can be ENERGY STAR certified yet have massively different figures in their performance rating. This is because climate plays a huge role in determining the performance rating in a window.
The ideal performance rating and the climate
The U.S. has a wide range of climates due to its size, and any performance rating will have to take that into consideration. Warmer climates will require a different approach than those of colder climates, and the two ratings that will have a vast change are the SHGC and U-factor ratings.
As previously mentioned, SHGC determines the amount of solar heat that passes through the window. Warmer climates would prefer this to be lower to keep living spaces cool. On the other hand, living spaces in colder climates would want the opposite effect, letting in more solar heat as a natural method of warming up the interior.
This also applies to the U-factor. Since a lower U-factor means better heat insulation, it works better for colder climates, while hotter climates would prefer a higher U-factor, allowing heat to escape and keeping the space cool.
The certification criteria are based on four different climate zones: Northern, North-Central, South-Central, and Southern (we will explore the regions in greater detail further down). Each region has its own U-factor and SHGC requirements to meet before being ENERGY STAR certified, and here are the figures:
The four climate zones
The four climate zones are roughly based on this map.
Northern climates are generally defined as areas with cold winters but with relatively mild summers. Heat retention in living spaces takes priority.
States that generally fall under this category are Alaska, Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, New York, Michigan, Wisconsin, Minnesota, North Dakota, South Dakota, Montana, Wyoming, Idaho, Washington, Oregon, and northern parts of other states such as Illinois, Iowa, Nebraska, and Nevada.
North-Central climates are mixed. Areas with this climate have both hot summers and cold winters. Windows certified for these areas must have a balanced rating to ensure that the living space is energy efficient in both types of weather.
States with North-Central climates are Ohio, Pennsylvania, West Virginia, Indiana, Kentucky, Virginia, Maryland, Delaware, New Jersey, Illinois, Missouri, Iowa, Kansas, Nebraska, Colorado, Utah, Nevada, and parts of Michigan, Wisconsin, Minnesota, and Wyoming.
South-Central climates are areas where the summers are hot, but their winters are mild. Windows here focus more on reducing heat within the living spaces.
States with South-Central climates are Texas, Oklahoma, Arkansas, Louisiana, Mississippi, Alabama, Tennessee, Georgia, Florida, South Carolina, North Carolina, and parts of Virginia, Kentucky, Missouri, Kansas, and New Mexico.
Southern climates feature hot and humid summers, with even milder winters. The priority of windows in this area is to let heat out of the living space.
States with Southern climates are Arizona, New Mexico, California, Hawaii, and southern parts of Texas, Nevada, Louisiana, Mississippi, Alabama, Georgia, South Carolina, North Carolina, Virginia, Maryland, Delaware, and Florida.
Shifting climates and accuracy
It is important to note that climates are inconsistent and can change yearly. Shifting weather patterns also mean that the efficiency of a window might vary as well. Furthermore, some states, such as California or Texas, have multiple climate zones, and depending on how far north or south, a specific window type will be required.If you are unsure about a state’s climate and ENERGY STAR requirements, ENERGY STAR provides a website for reference, not just for the state, but down to the specific county. You can see it here. Regular updates on states and counties are also listed in a spreadsheet that can be found here.
How Vistaza Can Help
If you were looking at the ENERGY STAR label above, you might’ve noticed that the label is for Vistaza products. Well, that’s because Vistaza is an ENERGY STAR partner and carries ENERGY STAR-certified windows.
We can assist developers in outfitting buildings with windows best suited for the specific climate zones, allowing for energy-efficient windows that provide large cost-saving benefits in the future.
