An interactive computer program that calculates monthly heating loads of buildings and the lifecycle cost of heating has been developed. The program is designed for residential and light commercial buildings. It incorporates passive heating features as well as conventional heating systems and is useful for determining the energy savings and economic benefits of various conservation measures.

The input and output format is flexible to allowing detailed specifications of building shape, construction, orientation, and location. The weather data base contains 244 North American locations; additional data may be added by the user. The outputs are monthly and annual totals of energy loss from components such as walls, roof, windows, etc. The economic analysis gives the life-cycle cost of heating, and includes the effects of the fuel inflation rate, mortgage interest rate, market discount rate, and federal and state tax credits for energy conserving measures.