When it comes to recommendations for energy efficiency actions after someone has had a weatherization team perform an audit on their home, replacing windows and tuning up the furnace or boiler are often on the top of the list. From an energy point of view, often you may hear, “a window is a big hole in your wall”. This is usually in the context of most Interior homes having exterior walls rated for at least 20R; yet windows of medium grade an average cost (with multiple panes and filled with gas) are around 4R.
Thus there are different gasses that can be used, different styles of glass, various films that can be added to reduce infra-red ray and a handful of materials to build the frames out of. Yet aside from the building materials and technologies of film application, a window’s insulative performance will be influenced greatly by the installation. It is very important to have the window opening prepared for moisture control. Using backer rod to fill space well and applying a caulking that won’t break up from being exposed at -40 degrees (F) in the winter and possibly in the 90’s during the summer are important aspects to a good installation. Also, the sealing and then integration of siding over the vertical wall sheeting is very important.
Though today’s windows are being made better out of recent advantages from research in the last couple decades, we still at best can get ~7 or 8R out of a window under the best of insulation methods. Most people cannot afford to pay a couple thousand dollars for one of these cutting edge picture windows, yet they can control how well or poorly the installation job is for their own home windows. How are your windows?