This paper presents the establishment of optimum design conditions and economic evaluation for solar hot water system. The aim of this study is to present thermal performance of solar heating systems and to determine their performance as a function of collector size, storage capacity, tilting of collector and other factors. By analyzing its performance under the various conditions, optimum design of solar heating system can be obtained. System performance are obtained monthly and yearly basis respectively. At the same time the economics of various systems are evaluated. For the computer simulation Mokpo, Kangnung, Chupungnyong and Seoul are selected for particular installation places. As a result, the optimal design condition of solar heating system considering the following factors such as installation angle of collector, capacity of storage tank, collector size in each place can be obtained as follows; (1) Installation angle of collector Tilt = lattitude (2) Capacity of storage tank Solar domestic hot water system : $45;1/m^2$ Multifamily solar domestic hot water system : $35;1/m^2$ (3) Collector size i) Solar domestic hot water system Seoul & Chupyungyong area : $11.52;m^2$ Mokpo area : $8.64;m^2$ ii) Multifamily solar domestic hot water system Seoul, Chupyungyong & Mokpo area : $345.6;m^2$ Kangnung area : $259.2;m^2$