Choosing the Right Glass for Replacement Windows
July 24, 2007
Look around new model homes or at the displays at home and garden shows and you'll find a dazzling array of replacement window styles and varieties of glass. Selecting the right replacement window at the best price for your local weather conditions and your home improvement budget can pay dividends in saved energy and maintenance costs.Understanding the window ratings system can help you refine your choices. There are U values and R values applied to energy efficiency ratings, and these are typically displayed on the window sticker. Since there is such a wide variation of temperatures across the country, you should determine the kind of ratings that best serve your home.
Simplified, an R value rating measures how efficient a single window component is at resisting heat loss. The higher the R value, the more efficient the window glass is in preserving your indoor temperatures without conducting outdoor heat and cold.
A U value refers to the rating for an entire assembly of parts in overall energy efficiency. This can be the telling factor in selecting the most efficient replacement windows. In this case, the lower the U value, the better the window is in fighting heat transfers.
Evaluating Replacement Window Ratings
The best thing to remember is that, for the price, the higher the R rating or lower the U rating, the greater the insulating value in your window. Ratings take into consideration the glazing materials, the number of glass layers, and the "tightness" of the installation.
If energy efficiency is your principal concern, you might consider buying what is called a "superwindow" -- a product known for low emissive surfaces (Low-E coatings), special gas fills between the layers, and multiple glazings. It carries a low U-factor, typically less than 0.15.
If you're comparing types of glass, it's a good idea to evaluate coatings. Low-E coatings reflect up to 70 percent of the heat blasted at your window without significantly reducing the amount of light that enters the home. There is also a heat-absorbing tint that can absorb up to 45 percent of incoming heat without reducing light.
Many manufacturers also offer heat-mirror film that looks clear to the eye, reflects incoming heat, and offers increased insulation. The film is rated by climate type, allowing for fluctuations of summer and winter temperatures around the country.