This chapter discusses the homeowner or the contractor/builder who wishes to determine the economic effectiveness of installing a solar water heating or space heating/water heating system on the roof of a house. The homeowner is generally most interested in the monthly costs of the heating system as reflected by the monthly utility bills. Therefore, a comparison of the monthly costs of a solar/conventional heating system with those of a conventional system alone is an appropriate form of analysis. Economic analyses are usually made on an annual rather than on a monthly basis. The more rapidly fuel prices increase, the greater the accumulated fuel savings resulting from the solar system and the more attractive the economics become. Typically, solar space heating systems provide from 1 to 1.5 therm per square foot of collector per heating season; solar domestic hot water systems from 2 to 3 therms per square foot of collector per year.