Definitions for "U-Factor"
a measure of the rate of heat flow through a material or assembly. It is expressed in units of Btu/hr-ft2-[ring]F. Window manufacturers and engineers commonly use the U-factor to describe the rate of non-solar heat loss or gain through a window or skylight. The lower a window's U-factor, the greater are its resistance to heat flow and its insulating value.
A measure of total heat flow through a window or door barrier from room air to outside air. Lower numbers indicate greater insulating capabilities.
The factor representing resistance to heat flow of various building materials.