There are two basic categories of pipe systems: one-pipe and two- pipe systems. In a one-pipe heating system all radiators are connected to the same pipe, which acts as both flow pipe and return pipe. This means that the temperature decreases along the pipe. For this reason, the radiators along the pipe line should increase in size correspondingly to provide the same heat output.
One-pipe system with vertical distribution
The water is distributed from above from the horizontal distribution pipe. A single air vent is sufficient at the top.
Since there is only one pipeline to the radiators, the system is visually more acceptable. This is an advantage in a system where the pipes are exposed.
One-pipe system with horizontal distribution
A one-pipe system where the water is piped horizontally is to be preferred in situations where it is undesirable to have a vertical pipe up through the rooms.
Such a system is more difficult to vent, so all radiators need to have an air vent screw.