Heat loss through windows primarily involves conduction. Conduction is the transfer of heat through direct contact between two substances with different temperatures. In the case of windows, heat flows from the warmer indoor air through the window and into the colder outdoor air. The thermal conductivity of the window material, as well as the thickness of the window, determine the rate of heat loss through conduction. However, convection can also play a role in heat loss through windows, especially if there are air currents or drafts.
