The shading coefficients (SC) and U values (overall coefficient of heat transmission) listed in the ASHRAE 1967 Handbook or Fundamentals and in earlier volumes of the ASHRAE Guide and Data Book have assumed natural convection only on the indoor side of glass surfaces. It is now found to be a frequently encountered practice to install supply registers in window sills or directly under windows so that the supply air will sweep the glass surface. While this will obviously have a beneficial effect in bringing the glass surface to a temperature which more nearly approaches that of the air conditioned space it is also apparent that it will increase the cooling load in summer and the heating load in winter. It was the purpose of this research to determine the extent of this increase and the relative effect of the 2 factors, air velocity and temperature, which cause it.