Let’s begin with a primer on what Low-E glass is. PPG provides a more intense description of Low-E glass at http://educationcenter.ppg.com/glasstopics/how_lowe_works.aspx. In a nutshell, the coating in Low-E glass minimizes the the amount of ultraviolet and infrared light that can pass through glass without compromising the amount of visible light that is transmitted. The coating can be applied as hard coat where the top surface is heated to almost melting and the coating is injected below the surface. This glass can be easily handled after it is cooled. The coating can also be applied on the surface of room temperature glass. However, the coating cannot be touched after it has been administered. This is a process utilized by Cardinal Glass. The soft coating is available in three layers, 180 (single), 272 (double) and 366 (triple). Each additional layers reduces the amount of ultra-violet and infrared more which provides fade resistance. At the same time, the solar energy from the sun is reduced thus providing cooler glass surfaces which is beneficial in the summertime. However, the drawback is that, since glass performs the same all year round, cooler glass surfaces will also prevail in the wintertime. In Canada, where more of the year is spent heating our homes than air-conditioning them, multiple coated glasses can prove to be a disadvantage. The beneficial passive heat from the sun that would help warm our homes in the winter is being blocked by these multiple coated glasses. This fact is supported by the substantially lower Energy Rating numbers ( as specified by Energy Star ) for multiple coated glasses in comparison to single coated glasses, whether soft coat or hard coat. My advise is to select a multiple coated glass like Low-E 366 if you have rooms in your home that are unbearable to be in because of excessive summer heat or that fade resistance is extremely important to you. Select a single coat glass such as a hard coat or 180 if you want to retain the benefit of passive solar heating in the winter.
I have been asked by many customers if a benefit exists to having vinyl window frames filled with foam. There are some companies that charge a substantial premium for this feature. A few years ago, I came across an article that dealt with this issue. The article has been repeated in many forum postings such as this post at http://www.vinyl-replacement-windows.com/forum/viewtopic.php?f=2&t=714. The testing and evaluation has been performed by Enermodal Engineering of Waterloo, Ontario. The result is that the net effect on the overall window is an increase of 0.1 improvement in total R-Value of the window. In comparison, selecting triple glazing over double glazing can improve the R-Value of the window by about 0.7; 7 times greater than the foam-filled frame feature. The foam filling is very visible and impressive in crosssection at trade shows, but performance should be the primary goal. As I tell my customers, common sense should also prevail. The largest area of the window is the glass, not the frame. Choosing your glass wisely will yield a better return on your investment than choosing the frame.