Until recently, the degree-day method of annual energy consumption was essentially the only method to estimate annual heating energy. With the increasing importance of energy conservation, the need for a more accurate energy calculation procedure becomes obvious. The large energy computer programs have met this need, but while these computer programs provide the necessary accuracy, they lack the speed and simplicity that the degree-day method once provided.

Recent attempts at improving the degree-day method have been aimed at modifying the correction factors, rather than improving the basic equation. And, because of the effects of internal heat gain on industrial and commercial buildings, the basic degree-day formula has been discarded for all but residential energy estimates. This paper attempts to develop a degree-day formula which can be used for commercial and industrial buildings.