Performed with the upper and lower wiring lines (see Figure 19).
In two-piped systems with upper setting, each heating device is served by supply and return pipelines. If we do not consider the cooling of water in the pipes, then we can assume that the water goes to all the heating devices with the same temperature.
In two-piped heating systems with lower setting, the supply and return pipelines are installed in the basement of the building or in special channels which are made in the floor of the first storey. In these systems, the warmth carrier goes to the heating devices, not from above downwards, as in the upper setting of the supply pipeline, but from below upwards. In other respects, the system works on the same principle as the upper setting of the supply pipeline. The air from the system with the lower setting of the supply pipeline is removed by means of the air line which is connected to the vertical pipelines and it removes air towards the air collector or through the air valves. To regulate the warmth output of the devices in two-piped systems on the supply to the heating devices, valves with double regulation are installed. On the supply and return vertical pipelines, in the places where they are connected to horizontal pipelines, valves for turning off vertical pipelines are installed in case repairs are needed. The expansion tank is the same as in the system with upper setting and is installed in the return pipeline before the pump.
Two-piped heating systems with low setting compared to the systems with high setting have the following advantages: there is not as much piping going through unheated rooms and warmth losses are decreased; and in the process of servicing the system, turning off particular vertical pipelines in case something goes wrong is more convenient because the valves on the supply and return vertical pipelines are located in the same place.