The hydronic oil fuel furnaces have weird pipe arrangements, which can be open or closed; then the piping system distribution may be a single pipe, more than one pipe, or more than three pipes.
These pipes carry water, back and forth, throughout the system and deliver steam to the radiators to produce heat.
There is no water loss in this system. The first type is the open piping system. This system has an expansion tank that opens to the atmosphere and a water loop system—hydronic heating that involves heating with the help of water instead of steam! It has a single pipe that runs throughout the system. When a room needs heat, the radiator heats the water, which, in turn, heats the specific area. The direct return piping allows the piping to run in a direct path, thus optimizing piping costs in the process… Larger hydronic systems use a reverse return piping design with a closed-loop system and a return header affixed to a remote hydraulic load. This design ensures the water flow and pressure distributed equally across the system. A closed piping system is sealed completely to avoid interference from atmospheric pressure. Another type is the 1-pipe arrangement which uses a single pipe to serve as both the supply and the eventual return line. This system is common in small homes. The third type is the four-pipe system. It’s simply a more than one-pipe heating and a more than one-pipe cooling system. It uses primary and extra units in massive industrial buildings, massive residential areas, and greater commercial buildings where zoning is required. In this system, the primary pump circulates water continuously throughout the building through the primary circuit… Consult a nearby heating, ventilation and A/C corporation or a nearby heating, ventilation and A/C corporation when purchasing, installing, or inspecting a hydronic system.