Aluminum single hung windows are certainly one of the most common types of windows found in North American homes. They are simple to operate, easy to install and affordable even for the smallest of budgets. So why doesn’t everybody use these windows then? That’s because, like any building material, they have their strengths and their weaknesses-and being the most energy efficient isn’t one of its virtues. So what’s the best energy efficient window choice for your new home, remodel, addition or window upgrade project?
Energy Efficient or Energy Vampire?
Aluminum windows have been given a bad rap over the years when it comes to their energy efficiency. That’s because when aluminum windows were beginning to become popular, energy efficiency wasn’t really an issue like it is today. Vinyl windows took some of aluminum windows’ market share because of the fact that aluminum windows were less energy efficient than vinyl. But it’s not because of the material (i.e. aluminum or vinyl)-it’s because of the way they were built.
Aluminum does have a slightly lower R-value than vinyl, but not really enough to make a huge difference. So why do many vinyl windows almost always have a better R-value than a typical single hung aluminum window? It’s because of these four main factors listed below:
Conduction- This is basically heat from the outdoor ambient air (or your homes heater) that travels through the glass and metal frame of a window. A direct transfer of heat like this is similar to feeling heat from a hot pan through an oven mitt. Conduction is slowed but never stopped. To combat conduction, window treatments like curtains can be used to stop this energy inefficient phenomenon from taking place. Shrubs, trees and other landscaping on the outside of the window can help reduce conduction on the outside of a structure.
Convection- The process of convection occurs when a large difference in air temperatures occurs between the inside and outside of the home. Hotter air loses its heat to the cooler glass surface and falls downward. Warmer air fills in the space and a circular draft of air begins to flow around the window, causing more energy to be lost in the process. A quality glazing or tinted window film will reduce over heating from convection.
Radiation- As infrared radiation from the sun passes through the window and frame; it excites the molecules within and generates heat. The more radiation allowed to pass through the window, the less energy efficient it becomes. The best way to combat heat from the sun is by installing a low-E argon gas double pane glass with a glazing.
Air Leaks- As air heats up from infrared radiation, it begins to cause a pressure difference between the outside air to inside air pressure. Wherever windows have air leaks (i.e. weather-stripping, window panes, poor installation) hot air will either attempt to escape the home (as in winter) or it will try to enter the home (as in summer). Air leaks are prevented best by quality construction and proper installation.