The passive type solar energy heating system for the classroom was investigated. A classroom in a primary school located at Gangnam-ku, Seoul was taken as a model classroom the heat balance equation was established. The temperature in the classroom and solarium were calculated from the heat balance. at clear days, the temperature in the classroom and solarium were measured and compared with the calculated values. The calculated and measured values for the temperature agreed with, in general, in the increasing of $20\%$ range. It was found that the smaller size of solarium could Provide the increasing of energy efficiency for the classroom temperature.