By Michael Tenhulzen
Special to The Seattle Times

One of the most popular types of glass is called low-emissivity or low-e glass. It uses a special coating to keep heat either in or out, depending on the time of year.

Q. What advice do you have for replacing windows?

A. Replacement windows are windows designed to fit into the same structure that the old windows come out of.

When considering which type of glass will work best for you, consider the R-value and the U-factor. These are ratings replacement-window manufacturers assign to their windows that tell you how efficient they are.

The R-value of a window indicates how well it insulates. These values go from 0.9 up and a window that insulates fairly well will have a rating of 3 or more.

The U-factor is how well the window does at keeping the heat in. In this case, the lower the number the better, so you want a value from 1.1 to 0.3. Only use single pane windows if heat loss isn’t a factor, such as detached garages or sheds. Double and triple-pane glass use panes of glass, hermetically sealed with airspace in between.

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