Low emissivity, or Low-E windows as they’re sometimes called, are windows that contain a highly reflective coating on the glass. That coating reflects both heating and cooling back into homes, which reduces solar heat gain in the summer to lower energy bills. In fact, the Department of Energy projects that installing Low-E storm windows saves the average homeowner somewhere between 12 to 33 percent on their annual utility bills.
That’s great for your energy profile—but it may not be so swell for your next-door neighbors. In rare cases, the reflective power of Low-E windows is so strong that it causes massive heat damage to neighbor’s homes. A number of complaints have emerged over the last decade, with homeowners claiming their neighbor’s Low-E windows melted their vinyl siding. Vinyl is essentially hardened plastic, so it’s temperature sensitive, just like plastic. In temperatures over 160 to 165 degrees, it can soften and eventually warp, droop, and ripple.
Luckily, it never gets that hot on Earth, so most of the time, vinyl makes a fine choice for external cladding. However, put it next to a Low-E window and the result could be disastrous. That’s because sunlight striking the specially-coated Low-E windows sometimes acts like a magnifying glass, concentrating the sunlight onto a single point. And for some unlucky neighbors, that point just happens to be located on the side of their vinyl-clad home. Today we’ll take a look at why Low-E windows cause heat damage, what to do about it, and how likely it is to happen in your home.
Understanding Why Heat Damage Occurs
Under normal circumstances, Low-E windows will hang for many years without causing any problems at all. In fact, the conditions that occur to give Low-E windows the power to melt glass are quite rare. The issue isn’t completely understood yet, but it results from differences in barometric pressure between the interior and exterior panes of glass in double paned windows (the majority of Low-E windows are double paned). This difference in pressure occasionally causes the windows to become slightly concave. That, in turn, magnifies the light reflecting off the windows—according to some accounts, the beam could reach up to 200 degrees Fahrenheit. And that’s definitely hot enough to melt plastic.
How Likely Is Low-E Damage?
That said, if you install Low-E windows on your home, you haven’t necessarily just bought a vinyl-melting laser beam (or signed up for an awkward conversation with your neighbors). There have only been a handful of cases reported, so you’re probably safe. If you’re worried about it, though, you can cut your losses by following these guidelines:
- Don’t install Low-E windows on a home that’s less than 20 feet away from the house next door, particularly if that house has vinyl siding.
- Carefully weigh the benefits of installing Low-E glass on windows that receive a lot of light through south-facing windows. The majority of cases have involved a home’s south-facing windows.
- Consider adding an arbor or other shading between your home and your neighbor’s. This will protect your neighbors from any potential damage—and it may reduce cooling costs in your home, as well!
- If arbors are not an option, consider adding a polycarbonate awning to the window to reduce glare. According to the Department of Energy, this also reduces solar heat gain by up to 77 percent on west-facing windows and up to 65 percent on south-facing ones.
- Check the warranty on your windows to see if it covers heat damage. Some manufacturers have removed heat damage coverage from their policies, so be sure to read through the warranty first before you make a final purchase.
Are Low-E Windows Still Worth It?
In the vast majority of cases, the answer is an emphatic yes. Heat damage only happens to a proportionally small amount of homes, when the conditions are just right. In the majority of cases, all a home receives as the result of installing are lowered heating and cooling bills, since the Low-E coating reduces heating and cooling losses by somewhere between 30 to 50 percent.
Spectrally selective Low-E coatings allow you to block heat-causing ultraviolet and infrared waves from the sun without limiting the amount of visible light allowed through the glass, like you might with tinted windows. That means more light indoors, while saving energy. And in some areas, Low-E coatings are required by local energy codes, as well.
If you follow the precautions listed above, you should be able to have your energy efficient windows without upsetting the neighbors. After all, you know what they say: good fences make good neighbors. In the case of Low-E windows, they may just be one way to avoid legal trouble, too!