Hiring a window installation company to replace some windows in your house? Do you live in an area that suffers brutally cold winter temperatures? Choosing winter-efficient windows can help keep your heat costs down in winter without also sweltering you out in summer.
There are three characteristics to look for when considering window efficiency: low-e, r-value / u-factor, and SHGC.
Low-e or low emissivity coating is a coating placed on the window pane by the manufacturer. The coating is clear and doesn't block out any incoming sunlight. But it does reflect some of the ultraviolet light that wants to come in with the sunlight.
There are different types of low-e coating available depending on how much heat you want kept in or out. A window with low-e coating only on the inside, for example, would work better at keeping heat inside your home and thus is better for homes needing more help heating than cooling.
R-Value / U-Factor
R-value is a measure of how heat resistant a window is while the u-factor is a measure of thermal conductivity. The u-factor is simply the inverse of the r-factor so a lower u-factor is good while a higher r-factor is good.
These measures come in handy when comparing similar models of windows for efficiency. Across all models, a triple paned window with an argon filling and a wood or vinyl frame and low-e coating is going to have much better r- and u-measures than a double paned window with an aluminum frame, no gas, and no coating.
Solar heat gain coefficient, or SHGC, refers to the ratio of solar radiation that makes it through the window. There are no good or bad SHGC scores. It simply comes down to where the window is and what you want the window to do.
A low SHGC score allows less heat through the window into your home but bounces more heat off, which essentially makes it a shading window. This means a low SHGC window would be great in an east-facing window that has no trees nearby and lets in a lot of direct sunlight. But a low SHGC window would be redundant on a west-facing window covered by a large awning or tree.
Another way to look at it is whether you want the window to primarily keep out the summer heat or lock in the winter heat. A low SHGC window is the better summer bet while a high SHGC window is better for winter insulation.
For more information, contact a local window installer such as Innovations Siding & Windows.