In general, windows take up a proportionately small area of thermal envelope. At the same time they are one of the most utilized parts of a home, as occupants use them for light, ventilation, passive heating or for aesthetic reasons.  In cold climates, windows can represent a significant heat loss, because of their low insulative value relative to the thermal performance of the other components of the building shell.  Conversely, windows can also provide valuable passive heat to a house.  Thus, having an appropriate window for the climate, coupled with appropriate placement, is important to maximize performance

The Cold Climate Housing Research Center provides extensive information on windows for structures in the circumpolar north.