Recently, an increasing interest in district heating system or combined heat and power(CHP) system has emerged rapidly. District heating systems are not only more energy efficient but also provide emergency backup to the power grid as well as the thermal network of a building complex. In this paper, the physical measurements such as hot water heating supply temperature and pressure were carried out by using numerous data loggers. In order to estimate the heating energy consumption, various measured data has been monitoring from mechanical rooms of apartment housings with district heating system in Ko-yang district, Kyung-gi province to data gathering place(University) in Seoul through the internet on the hourly basis. Since 1970s, the insulation standard has been improved through irregular revision many times. Thus, this paper is to show how the heating energy consumption were effected by the variation of insulation standard of residential buildings in Korea. In other words, the purpose of this paper is to understand the effect of the enhancement of overall transmittance coefficient(insulation standard) upon the heating energy consumption of residential buildings. Furthermore, it can be suggested as the basic data assessing the policy measures for heating energy savings in apartment housings.