Aluminum Replacement Windows
Aluminum windows are rarely used for residential purposes anymore but are common in commercial applications. The reason for that is builders are willing to give up heat loss/ gain ramifications for the strength that is needed for large openings. Aluminum windows are obviously made of metal, which is a good conductor of differences in temperature. Thus if it is extremely cold outside that cold, (or actually absence of heat) will be transferred through the aluminum into the residence. Conversely, if it is very hot outside that heat will also be transferred into the building.
You do not want to confuse aluminum windows with windows actually made of aluminum. There are essentially four types of materials windows are constructed from; Aluminum, Vinyl, Wood, and Composite (such as fiberglass). Wood is a popular material but it is subject to the outside elements, and will need periodic painting and maintenance. To combat this, window manufacturers cover the exterior of the window with aluminum. This protects the exterior, and provides a wood finish for the interior which is quite popular.
In the US today, there are thousands of aluminum windows being replaced every day, with more energy efficient vinyl products.