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Trunk and Branch Residential Plumbing Layouts
For decades, trunk and branch (T&B) plumbing layouts have been used by plumbers and home builders for water distribution using iron pipe, copper pipe, and rigid pipe. Trunk and branch plumbing layouts use a main trunk line to supply various branch take-offs to specific fixtures.
The trunk line services numerous branch lines, each branch lines serving generally one to three closely grouped outlets, such as in a bathroom where there may be one or two sinks, a toilet and a shower.
With trunk and branch plumbing the plumber usually uses rigid pipe, and generally follows the beams and trusses when installing the piping. This means extensive use of elbows and longer pipe runs than if the pipe was run directly from the water heater to the fixture.
Recirculating systems don't work will with trunk and branch plumbing layouts, since they don't include the branch lines in the circulating loop. (See Fig 1) Demand hot water systems suffer similar problems, although one could use multiple demand pumps.
A relative newcomer to the residential plumbing system is the PEX manifold plumbing layout. A manifold system is similar in a way to the trunk and branch system in that it has a single trunk line leading to a manifold which in turn sends a single branch line to each fixture or closely spaced group of fixtures such as in a bathroom. (Fig 2)
In some situations the manifold type plumbing layout can work well with recirculating systems and demand hot water systems. For example, if the trunk lines are long, a pump could be placed at the manifold to rapidly fill the trunk lines. The branch lines being much smaller in diameter hold a much smaller volume of water and thus have a high flow rate.
With high flow rates the deliver is rapid and wastes only a small amount of water.
These systems are sometimes referred to as remote manifold systems. These systems are sometimes combined into a hybrid system, for instance, it could have two or three trunk lines with a remote manifold at the end of each trunk.
All kinds of combinations are possible. A single trunk line could have several flow-through manifolds and one at the end of the trunk line.
With PEX manifold systems shut off valves are often located at each outlet on the manifold allowing you to turn off individual fixtures for repair or replacement without shutting off the water to the whole house.
PEX piping systems make it ideal for use in home-run plumbing systems. In this design, all fixtures are fed from dedicated piping that runs directly from central manifolds. The hot water manifold should be located in close proximity to the hot water source to ensure fast and efficient delivery.
Because inline fittings are eliminated, pressure losses along the line are reduced, allowing the piping size to be reduced for certain fixtures. Three-eighths-inch piping may be used for lower flow applications and 1/2-inch piping is recommended for higher flow applications.
If the manifold is installed using a valve at each outlet, many plumbing codes do not require a second valve at the fixture. This speeds installation and adds convenience.