How does it work?
The water heats up inside the boiler and is sent to the radiators by a pump. The water from the pump goes to each radiator; in turn, the water from the last radiator goes back into the pump. In the early versions of this system, the pipes at the beginning had to be much broader. This is so the radiators at the end could receive sufficient heat. This led to an unbalanced system where the radiators closest to the boiler were very hot, and the radiators at the end of the system were, at best lukewarm.
Improving the system
By putting a bypass on each radiator, the one-pipe system can work better. The water doesn’t go from one radiator to the next. Instead, a bypass gives the pumped water two ways to go. Using radiator valves, they could make sure that each radiator was at the same level, depending on where in the system it got its hot water.
The radiator valves are set to restrict flow more when the radiator is close to the boiler. By doing this, it would send more hot water to the farthest radiator before the water lost too much heat. Even though this system worked much better, it still had some flaws.
The one-pipe system has some flaws.
Heat loss is the main problem. This might not be a big deal on a small system, especially if all the pipes are insulated and there aren’t many bends in the pipe. But this is the Achilles heel for larger heating systems. No matter what you do to stop heat from escaping or improve circulation, a large system with only one pipe will have too much temperature difference. This led to two pipe systems that are still used today.
