by Marie of Flo-Pac, LLC
A two-pipe direct return system and a two-pipe reverse return system are similar in function and require the same parts (such as piping and balancing valves), but there are a few key differences in the way the return piping and the terminals are laid out. Each system has advantages and disadvantages.
How Does a Two-Pipe System Work?
A two-pipe water heating system is centered on two main pipes: one to deliver water (the supply) and one to return the water to the boiler (the return). In addition to the two mains, each terminal connected to the main will also have supply and return pipes. Unlike one-pipe systems, the mains of a two-pipe system will provide water that’s a consistent temperature to each terminal – so this setup can be used for water systems in large or small buildings.
In a two-pipe direct return system, the return piping takes the water back to the pump by the shortest possible path. Since the main piping is the most difficult and expensive piping to install, this has the advantage of keeping the mains shorter. A direct return system also routes terminals so that their locations on the supply and return pipes correspond; that is, the first terminal on the supply is the first on the return, and the last on the supply is the last on the return. A direct return system requires less main piping, but because flow will be uneven (favoring the front terminals), the system will require manual or automatic balancing valves.
A reverse return system is routed to be the opposite of a direct return: the first terminal in the supply is the last terminal on the main and vice-versa. This is possible because the return is set up to be the same length as the supply, and it often runs in a circle around the building. A reverse return system means that supplies and returns are the same length throughout the water system, making for a more even water flow to all terminals. However, unless the system is designed to be self-balancing, balancing valves will still be necessary to ensure consistent water flow.