Precise control of room temperature for floor heating systems is a key step toward intelligent heating, which is of great significance in achieving thermal comfort and energy savings. Generally, the room temperature is controlled by thermostats that are placed on a wall, far away from the occupied zone. This may cause large temperature control deviation and cannot satisfy thermal comfort of the occupants. Based on the theory of the building thermal design, this study investigated the factors influencing the heating room temperature and temperature control deviation by combining a field experiment with a numerical simulation, providing a thermostat installation location strategy. The results show that air infiltration and solar radiation are the two main factors affecting the indoor temperature field. For conventional heating systems widely used in severely cold regions of China, it is not recommended to install thermostats near the occupants, but rather on the walls. The installation location should comprehensively consider room size, air infiltration, and solar radiation. To avoid the influence of outdoor factors and internal heat sources, 1.5 m can be used as the optimal installation height. These findings provide reference for the precise control of room temperature for floor heating systems.