U-Factor. The heat transfer per time per area and per degree of temperature difference. The U-factor multiplied by the interior-exterior temperature difference and by the projected fenestration product area yields the total heat transfer through the fenestration product due to conduction, convection, and long wave infra-red radiation. Expressed here in units of Btu/h·ft2·ºF.
U-Factor. The rate of non-solar heat loss or gain through a material or assembly. Expressed here in units of Btu/h·ft2·ºF.
