Is It Getting Hot In Here?
Science and technology are so very closely interwoven into the things we encounter every day. So much so, that we often take for granted how they’ve changed things, or have never really noticed the changes at all. Even simple things, like windows, have been changed by different technologies over the years, to the point where they’re no longer just holes in the wall for looking out of your home, or letting the light in.
The windows of your modern home affect your home’s overall energy efficiency, and the entire year’s energy bill is directly affected by the state of your windows. These days, we’re a bit savvier about how damaged, poorly chosen, or badly installed windows, just about guarantee that you’ll be spending more than you should have to.
The converse also holds true: the right choice of windows, in good repair and correctly installed, will reduce your overall energy expenditure, in some cases by as much as 40%. Whether you’re looking to fix up your windows, or are looking to replace them altogether, a more intimate understanding of window terminology, and how, all put together, it affects you, can make the difference between the former and the latter.
A window’s energy efficiency is a measure of how much heat (or, during the summer, cooling from the A/C or other similar sources) is gained or lost through the window. It is also a measure of how much sunlight passes through (and, indirectly, how much is reflected back), which also affects the temperature within your home. The National Fenestration Rating Council, or NFRC, tests, certifies and labels windows, as well as doors and skylights, based on their energy efficiency performance. The NFRC label provides an accurate determination of a window’s energy properties, and allows you to compare the energy efficiency of different products.
A window’s U-factor is a measure of how much non-radiant heat (i.e., not directly from the sun) it allows to pass through. The NFRC rates U-factor for the entire window assembly, not just the glass alone. The lower the U-factor, the more energy-efficient the window is, keeping more heat in when it’s cold, and keeping more heat out when it’s warm.
The Solar Heat Gain Coefficient, or SHGC, complements the U-factor and represents how much sunlight passes through, contributing to the heat in your home. The lower the SHGC, the less solar heat passes through and the more shade the window gives. A window with a higher SHGC helps provide more heat during the winter, while one with a lower SHGC blocks more heat due to sunlight in the summer.
Air leakage is a measure of how much air passes through the window, even when closed. The higher the air leakage, the more hot air escapes during the winter, and cool or cooled air during the summer, which will affect how much energy is needed to adequately heat or cool your home.
Coming soon is Part 2, where we will discuss the various types of windows.