The rate of heat loss is indicated in terms of the U-factor of a window. The lower the U-value, the greater a window’s resistance to heat flow and the better it insulating properties. In other words, the U-factor is used to express the insulation value of windows.
Solar heat gain provide free heat in the winter but can also lead to overheating in the summer. How to best balance solar heat gain with an appropriate SHGC depends upon the climate, orientation, shading conditions and other factors.
Insulated glass refers two pieces of glass that are sealed to a spacer, providing an air pocket in between. This results in better thermal performance and reduces condensation by keeping heat inside and cold outside.
Low-e stands for low emissivity and is the relative of the surface to emit energy by radiation. In layman’s terms, low-E reflects heat energy and stops it from passing through. Low-E glass is just a microscopically thin, transparent coating – it is much thinner than a human hair – applied between the panes of glass that reflects long-wave infrared energy (or heat).
Argon and Krypton are the gas fills used most often to displace air between the panels in windows to increase a windows thermal performance. Both gases are invisible, non-toxic gases which work better than atmospheric air to lower thermal conductivity.