This paper investigated the energy saving potential of the timely heat regulating approach for classrooms, a type of high density occupancy building spaces. Taking a typical lecture room in Harbin, China as an example, both experimental testing and CFD simulation were carried out to look into the space temperature and heat supply. Experimental results showed that the room was at the higher than expected temperature which caused unpleasant thermal uncomfortable, and the corresponding average heat supply rate reached 62.3W/m². The suitable average heat supply rate would be 28.7W/m², and under this condition, the room space would be able to remain at a pleasant thermal condition, and the system operation would achieve 53.8% of energy saving. By applying this method into the lecturing buildings in the whole range of China, estimated energy saving would be equivalent to 3.85 million tons standard coal.