I love looking through clean windows, but washing windows is among my least favorite chores. So when I saw Andersen’s High-Performance Low-E4 windows at the International Builders’ Show last February, I knew we had to test this new product as part of October 2007 report on windows. The sunlight-activated titanium-dioxide coating on the glass is supposed to create windows that, claims Andersen, “stay cleaner, dry faster for easy cleaning and that have up to 99% less water spots.”

Five months after the Builders’ Show I found myself on the roof of our Yonkers, New York, headquarters with Ed Perratore, one of our senior editors, and Rico De Paz, a Tech department project leader. We were examining two Andersen windows—one with the Low-E4 glass and one with regular low-e glass—to see whether we could identify which had Low-E4 glass. At that point the windows had been exposed to the elements for three months as part of our testing.

We looked at the exterior glass of each window from a few feet away and then scrutinized each one from up close. They appeared the same—one was not any filthier than the other. We also ran our fingers across the glass on each to determine whether one felt grimier. We still couldn’t tell them apart. Finally, we looked through the interior side of the windows. Again, one wasn’t noticeably dirtier than the other. In fact, neither was particularly dirty.

Our conclusion: When it comes to window cleanliness, it’s not worth the extra money to upgrade to the Low-E4 glass; in our tests, Andersen’s standard low-e glass stayed just as clean.—Celia Kuperszmid Lehrman

Essential information: Look for our special report, Save Hundreds on Energy Costs, in the October 2007 issue, on sale in late August. It includes full reports on windows, space heaters, compact fluorescent lightbulbs, and much more. Visit GreenerChoices.org for the latest news on environmental issues and expert advice on ways to save energy and money every day.