By focusing on several calculated factors, ENERGY STAR has made it easier to pick out the energy-efficient windows, doors, and skylights that are most appropriate for the climate where you live. Lowered heating and cooling bills and reduced energy waste seem like great ideas—and they are—but it pays to keep in mind that a window meant for the Dallas heat and sun won’t be a match for a Chicago winter. You certainly won’t want a window trapping heat where it isn’t wanted or letting that cool air escape at summer’s peak. To help consumers all across the country get the most energy-efficient windows and skylights, ENERGY STAR divided the US up into four zones: Northern, North-Central, South-Central, and Southern. These zones are based on climate and take into consideration such meteorological events as rain, temperature fluctuations, and humidity, among other factors.

So what does this mean? Basically, when shopping for new ENERGY STAR-rated windows or skylights, be sure to purchase products rated for your Climate Zone, as the specifications are different for different zones. If you’re not sure what zone you live in, visit ENERGY STAR’s website.

Northern Zone

The Northern Zone encompasses the largest portion of the continental US of any zone in addition to Alaska. Products rated for the Northern Zone are usually designed to keep heat inside the home and allow more heat to come through the glass of a window or skylight. If you live in the Northern Zone, check the U-factor of the product you’re interested in purchasing. The U-factor measures how much heat is lost from a window; the lower the U-factor, the more heat is retained. As Northern Zone areas have colder winters, residents of this zone may want to make sure that they’re buying the right U-factor-rated windows to ward off the winter chill.

North-Central Zone

The North-Central Zone covers many of the Mid-Atlantic states and snakes its way through the lower Midwest and parts of California. The climate in the North-Central Zone tends to be warmer than much of the Northern Zone, but it’s not as humid and rainy as the Southern Zone. Residents of this zone should look for an all-purpose window that has strengths in retaining heat in the winter and keeping homes cool in the summer.

South-Central Zone

The further south you live, the hotter and more humid the weather, so residents of this zone will want to look for ENERGY STAR windows and skylights that promote cooling the home. This is the second-biggest zone, and it covers most of the Deep South as well as much of Texas and Oklahoma. These areas can still see cold winters, so a secondary strength in keeping the house warm in the winter is recommended.

Southern Zone

The Southern Zone is the smallest zone and covers areas near the Gulf Coast, including all of Florida. Windows and skylights rated for the Southern Zone have a low Solar Heat Gain Coefficient rating, a factor that keeps rooms from getting hot from direct sunlight. They also may have a higher Visible Transmittance rating, meaning more sun is blocked, as well as a high Condensation Resistance, as these areas tend to be wet and humid. For more information on what certain labels mean for your windows’ efficiency, check out our blog on window energy-efficiency labels.

What About Doors?

ENERGY STAR-rated doors are judged a bit differently than windows and skylights. Instead of being classed into zones, doors are rated by an independent, third-party organization called the National Fenestration Rating Council, which sets industry performance standards for windows, doors, and skylights. If a door is ENERGY STAR-approved, it should be appropriate for any climate.

Before investing in new windows, skylights, or doors, it’s important to understand which ENERGY STAR Climate Zone you live in so that you can make the best decision for your home. Whether you’re dealing with a frigid winter or an unbearably hot summer, you should stay perfectly at ease in your home with the help of the right windows and doors.