Finding different thermal features for your windows may seem like a daunting process. Many different coatings, spacing, construction materials, and a variety of other factors all go towards determining the thermal efficiency of the window. The following text is designed to help you get an idea of what affects what as well as the more important factors to consider about thermal efficiency of windows.
The construction materials will play a large part in the base efficiency of a given window. Wood, fiberglass composite, vinyl, and aluminum all have different values that may be more or less appropriate to a given location. Replacement windows designed to help stave off the bitter cold of Montana do not need to have the same qualities that one would look for in Southern California, for instance. Determining your price range and appropriate materials are a good first step.
One major area that can allow thermal energy transfer is the gaps around the edge of the window sashes where they glide in place. The deeper these gaps are the better. The reason is that the weather-stripping on the edges of the sash can seat deeper into the frame and help to keep the air separated. Shallow channels will be more leaky and allow a greater thermal energy transfer between the interior and outdoors; something you want to avoid for maximizing efficiency.
Window glazing can be a confusing term as it can refer to a few different things. It's most common use is it refers to the actual panes of glass in the window. A multiple-paned window may be called a 'glazing solution' which is not meant to infer a liquid, but rather a solution to a problem. The glazing of the replacement window will largely help determine the overall efficiency of the window unit. Multi-paned glazing units are one of the leading areas for improved thermal efficiency. Double-paned glass with an inert gas filling of Krypton or Argon can dramatically increase the comfort level and maintainability of the interior climate. Triple-paned glass with an inert gas insulator filling offers a much more efficient solution but the price tag for them climbs higher. At minimum, one would want double-paned glass.
The glazing itself is often treated with different types of solutions to give the windows their own performance. These treatments can do things such as allow or block energy transfer from the interior or exterior, block damaging rays from the sun while allowing light in, or simply harden up the glazing to make it more resistant to damage. The manufacturer that you choose will normally have different glazing coats available so that a homeowner can find exactly what they need.
Proper installation of replacement windows can make a large difference with their thermal efficiency. If a window is improperly installed, it will leak air around it and allow the free exchange of air from both sides of the window. This guarantees that it will be an inefficient window no matter what positive qualities the windows have. These gaps between the framing and edge of the replacement window can allow weather to work its way in. The wood in the frame will be exposed to decay and mold which will only create more gaps and cause the window to leak like a sieve. Leaking windows have very poor efficiency and will not permit a homeowner to enjoy the thermal options they have on the window itself.
This makes installation one of the most important, if not the most important, part of thermal efficiency for replacement windows. If you intend to Do-It-Yourself, be sure that you are comfortable with the project and the size of it. While you may be able to save 20% or so on the final cost of the windows by choosing to do it yourself, the potential for loss is far greater down the road. Rebuilding an entire window frame unit can run into the thousands of dollars even for just a single unit.
Properly sealed and installed windows will allow the thermal features of the windows to do their job at keeping your home comfortable and energy-efficient.