True-divided-lite windows lose more heat.
Heat loss is highest at the edges of window glass. True-divided-lite windows lose more energy than windows with internal muntins because there are many more edges where heat can escape. Simulated-divided-lite windows, with the muntins sandwiched between sheets of glass, retain the thermal performance of the larger glass size. Because National Fenestration Rating Council ratings are not based on divided lite windows, they may overstate the thermal performance of divided-lite windows.
For a lot more information, see Green Building Advisor’s window page:Windows: Glass, Ratings, and Installation
—This GREEN BUILDING TIP is from Green Building Advisor’s Strategy Generator.
Build a tip sheet for your green building or remodeling project under the Strategies & Details tab.
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Energy saving windows don't bridge the indoors and out Placing the grills between the layers of glass keeps them in the warm zone and eliminates the thermal bridge of true divided lite windows.
