If you look at how much heat is lost out through a skylight (as we did two months ago in this column) and how much is gained, you discover that for most orientations with low-e, argonfilled units there is little or no energy penalty. In fact, even plain old double glass skylights aren't all that bad. I think there are a couple of reasons skylights got a bad energy reputation. First, in the old days, they were built on site and weren't insulated or sealed very well against air leakage. Second, many of them were built with or later developed water leaks. Well, weatherstripping and flashing have been taken care of by the manufacturers of modern skylights. That
