Energy Efficiency Values that Matter for Your Windows This Winter

Jan 09, 2018

Windows Installation in Westchester

How can energy efficient windows keep you warm in Westchester this winter?

Energy efficient replacement windows are the buzz this year when it comes to home windows. Many homeowners enjoy the benefits gained from energy efficient windows like lower energy costs, lighter carbon footprint, a more insulated home and even tax credits that come with energy efficient windows. And there are several ways to measure the energy efficiency of replacement windows to ensure quality insulation and efficiency.

But each season brings different challenges for your windows. Now that it’s winter, home insulation and natural light are more important than ever. So what energy efficiency values measure your winter’s performance specific to winter? There are three particular measures in winter that you need to look out for: Air Leakage, U-Factor, and Visible Transmittance.

Air Leakage

Air Leakage (AL) measures how much air from outside is able to leak through the window into the home. It is measured on a scale between .1 and .3. In winter, the higher the air leakage, the more likely the window will cause a draft in your home or that window condensation will form on your window. Window condensation tends to occur when the cold air from outside meets the heated interior of the home on the interior window glass. The window will become foggy and damp, and this can often lead to mold and mildew.

Energy efficient windows use double or even triple panes, often with gas fillings in the spaces in between to slow the flow of air before it reaches the interior glass. This stops drafts and window condensation and keeps your home warm and comfortable, even on the coldest days.


U-Factor is the window’s ability to keep heat generated inside the home from escaping outside. It is measured on a scale between .20 and 1.20. Again, the lower the number, the more efficient the window’s performance is. If the U-Factor is too high and too much heat escapes the room, homeowners often have to crank up the heating unit to keep the room comfortable, and that will cost them at the end of the month. Fortunately, the same gas fillings and multiple panes that keep cold air from leaking through retard the flow of hot air from getting out, so you can stay cozy and warm without putting a strain on your HVAC costs.

Visible Transmittance

Visible Transmittance is the amount of light from outside that the window lets through. In winter, we tend to spend less time outside and are deprived of natural light more than any other season. This can have a profound effect on our moods, causing seasonal affective disorder and decreased energy. Thus in winter, it’s important to have windows with strong visible transmittance so that even during the indoor months, you’ll still have ample natural light shining through. Visible transmittance is rated on a scale between 0 and 1 with the higher score denoting stronger performance.

The position of the window, type of window, and glass coatings all factor into visible transmittance. For instance, clerestory windows–often awning windows placed high on the walls–are often used to “daylight” a home, as they allow natural light to flood downwards into the room.

Your local replacement window experts at The Door Store can answer any questions you might have about the energy efficiency of windows or what energy efficient replacement windows are best for your Westchester home. Just give us a call at (630) 495-0100 or contact us online for more information.