Basic steam heating system parts
The typical residential steam system includes a boiler to produce steam, radiators to release the heat from the steam into the room, and the piping connecting the two.
The boiler usually burns gas or fuel oil to produce heat to raise the temperature of water to the boiling point.
In order to properly control the system, three basic components are required. A thermostat tells the system when heat is required. A pressuretrol turns the burner of the boiler on and off based on the pressure in the system. This is generally set at between 1 & 3 psi. This setting impacts not only comfort but also the responsiveness, noise level, fuel economy, and life of the system. Generally speaking, the lower the pressure is the better it is for the system. In a water based system, a pump circulates the heat while in a steam system it is accomplished by the pressure of the steam. Enough pressure is required to overcome the friction of the pipes. A low water cutoff (LWCO) is the third basic control and its purpose is to keep the boiler from operating without water in it.
A pressure relief valve ("pop safety") is also added to the system to protect from overpressure due to the boiler failing to shut off. Before these were installed, a steam boiler could explode.