This is probably due to the pressure, which in the heating system of apartment house may be not only high but also low. In the latter case, this leads to less effective work of the radiators. Simply put, they are worse than heat. Why is this happening?
The volume of heat, given out by the room heating devices, depends not only on the temperature of the coolant, but the number coming into the unit of water. In turn, the amount of water that can be passed through the pipeline to the device, depends on the circulating pressure causes water to move along the tube.
In this case, the water meets the resistance caused by friction of the walls of pipes, and in addition there was also the local resistance, which include bends, tees, crosses, etc.
In the radiant heating system can be used as a natural circulation of water, and forced (requires a circulation pump).
