coefficient K

CONT: U-VALUE. The overall heat transfer coefficient or thermal conductance of a building wall, floor, ceiling, roof, or other element; of piping or tubing carrying heating or cooling fluids; or of heat transfer equipment. The U-value is normally applied to a cross-section of more than one material and considers the film conductance and air. The total heat transfer can be estimated as the product of U, surface area, temperature difference, and time.