Windows have energy ratings given by the National Fenestration Rating Council. The U-factor measures how effective your window is at reducing heat loss. The lower the rating, the more efficient the window. The Solar Heat Gain Coefficient (SHGC) measures how much heat enters from the sun. There’s also the Visible Transmittance (VT), which measures how much natural light enters your home.
The lower your U-factor, the better, but your SHGC will depend on your local climate. If you live in a colder climate, then you would want a window with a high SHGC rating to let heat enter your home through a south-facing window. This will allow more sunlight to come through and help keep your home warm during the colder months. In a warmer climate, though, this could increase your cooling costs.
Many homeowners also assume the same rating works for every window in the house. In reality, the direction a window faces changes how it performs. A south-facing window can bring in helpful winter sunlight, while a west-facing window may take in strong afternoon heat during summer. Choosing different SHGC ratings for different sides of your home can help you balance comfort and energy costs.
How Your Local Climate Affects Window Selection
The U.S. Department of Energy provides some guidelines for energy-efficient windows. Depending on where you live, certain windows may not be the best choice. A window that would be great for Miami may not be the best choice if you live in the Midwest.
Many people experience extremely cold winters and extremely hot and humid summers in places like St. Louis. You will need windows that are efficient but can also reduce solar heat gain. A company offering the best replacement windows in St. Louis understands the weather in your area and can advise you on which ratings would be best.
Why Energy Star Certification Isn’t Enough
Windows with an Energy Star certification have to meet certain criteria to be considered energy-efficient for your climate zone. However, Energy Star-certified windows can still vary. They can have different U-factors, SHGC ratings, and frames.
The frames of your windows can make a difference. Aluminium window frames are popular due to their modern and slim design. Fibreglass frames will not expand or contract as much with temperature changes, meaning they can provide a tight seal. Choosing the right material can help improve efficiency.
It also helps to check the label on the specific window you are buying. The Energy Star logo is a good sign, but the individual U-factor and SHGC ratings will tell you how that window will perform in your home.
Endnote
Consider your local climate, window orientation, and frame material. Windows facing north in a colder climate will generally benefit from a low U-factor. Windows facing south may benefit from controlled solar heat gain.
Choosing the right glass specification and frame material can help increase efficiency. Knowing the energy ratings will give you a good starting point, but understanding which ratings will benefit your home will help you make a better decision.
Holding a Master’s in Architecture from the University of Texas at Austin, Emily Rodriguez has dedicated more than two decades to the art and science of building renovation. Starting her journey in historic preservation, she developed a profound respect for blending old with new in building design. Emily became a vital part of our team in 2019, renowned for her insightful and innovative renovation tips. She has been leading our DIY home improvement series since ever since, where she shares her wealth of knowledge in turning outdated spaces into modern havens. When not engaged in writing or consulting, Emily is a passionate advocate for heritage conservation and enjoys exploring vintage architecture, a hobby that complements her professional expertise.
