A double glazed window with a low-E coating has about the same insulating value as an uncoated triple glazed unit. The low-E coating alone improves the R-value from R-2 to R-3.
There are different types of low-E coatings with different characteristics such as emissivity, light transmittance and solar heat gain co-efficient. Generally speaking in Canada, the coating of choice would be for emissivity to improve the energy efficiency of the window. Care must be taken to ensure the right coating is specified for the right window application.
