A tilt-in, double-hung, insulated replacement window, isolated on white, with paths.

If you’ve started looking for new windows for your home, you may have come across what seems like a whole alphabet of abbreviations. We want you to be completely confident in your choice of new windows which is why we’ve put together these simple explanations of the most important acronyms and terms you’ll see and hear when evaluating window options.


Most of the terms you hear in reference to windows are determined by the NFRC, which stands for National Fenestration Rating Council. The NFRC is an independent non-profit organization that rates all new construction and replacement windows. They place their label on every window they evaluate so you can compare one window line or brand to another and easily determine which one is more energy efficient among other things. You will also be able to see if the window is ENERGY STAR® rated for northern Virginia which means it meets the minimum standards for insulation.

The Label’s Terms

The label has five different ratings. They each tell you something different about the windows. Most use a 0 – 1 rating with a lower number being more energy efficient.

  • U-Factor – This helps you understand how well the window insulates. Lower numbers indicate less heat escaping your home in winter.
  • SHGC – If you want to keep the sun’s heat out of your home, you want a lower value here as well.
  • VT – Although this still uses 0 – 1 scale, a higher number actually indicates more natural light. This doesn’t have anything to do with the window’s energy efficiency but rather a personal preference.
  • Air Leakage – Just as it sounds, this refers to the amount of air that leaks around the window frame and sashes. Again, a lower number is better.
  • Condensation Resistance – This rating isn’t done on the 0 – 1 scale and doesn’t impact the energy efficiency, it simply speaks to how well the window resists condensation. A higher number resists condensation better.

Windows Unlimited Can Help

If you’re looking for new windows call Windows Unlimited. We want to help you make an informed decision when it comes to your new windows. As a locally owned and operated window company, we know which windows are best for the communities in Northern Virginia. We’ll help you choose the best style and rated window for your budget and home. Call us today at (703) 468-4769 or fill out our contact form.