Many homeowners have the misconception that installing windows and doors in the winter is a bad thing, holding off because they are afraid too much cold air will get in the house or they will get a poor installation.

The process goes fairly quickly because new products are all prepped for the installation. The old window is taken out, the opening cleaned and any alterations are made, such as replacing rotted wood or putting in a sill pan. Then the window is placed into the opening, leveled and secured.

If there are multiple windows involved, winter installation is done one at a time to reduce heat leakage. In the summer, of course, multiple windows can be taken down at once.

http://greendale.patch.com/blog_posts/nothing-to-fear-about-cold-weather-window-replacement