By Chuck Ross
Centralized control seems to be the future for residential building systems, with advances such as structured wiring and home-automation systems tying oversight of HVAC, security and lighting to easily accessed panels. Manifold plumbing systems are seeking to bring the same degree of centralization to plumbing design by feeding all fixtures from a single multi-port receptacle. Proponents say that when used in the right applications, the approach, which uses 3/8-inch cross-linked polyethylene (PEX) piping, can save installation time, as well as water and energy, over traditional 3/4-inch copper pipe designs.
"It's lightweight, doesn't corrode and it can be fixed much more easily and replaced much more easily," says Carlos Martin, an engineer and administrator for the Partnership for Advancing Technology in Housing, a public/private effort to improve housing design and construction. The group included manifold systems in its Resource-Efficient Plumbing "Tech Set," a series of Web-based resources presenting new ideas for building-system design.
The use of smaller pipe is possible because each pipe run serves only a single fixture. For hot-water piping, this smaller diameter can mean less water is wasted flushing cold water from the pipe and less energy is required for hot-water heating. In addition, each fixture has its own shut-off valve, so maintenance to one fixture doesn't affect how others operate. And PEX piping only requires fittings at each terminal connection, with no intermediate tees and bends.
Out with PB, in with PEX
Manifold designs first emerged 20 or so years ago, in the days of polybutylene (PB) pipe, according to Joe Wiehagen, a senior research engineer at the National Association of Home Builders Research Center. PB pipe may be gone, but PEX-based manifold systems appear to be on the rise, with products now showing up on Home Depot's shelves.
"They're great systems in the right application," says Kevin Flannery, president and chief executive officer at North Salt Lake City, Utah-based Shamrock Plumbing. He sees small- to medium-sized houses as being especially good targets for manifold systems. In addition, he says, his firm has installed numerous manifolds in multi-unit hotel and apartment buildings. In these cases, he'll run larger supply lines to a floor or hallway, then place manifold blocks for each unit above the hallway ceiling.
This kind of hybrid approach also is best in larger single-family homes, experts say, where long piping runs could exceed recommendations—and, in some cases, code requirements—for 3/8-inch pipe.
At the NAHB Research Center, Joe sees that as an imminent trend. "It's something the industry is starting to talk about."
Though ease of installation is touted as one of the benefits of manifold designs, those with experience say that working with PEX requires understanding some basics, such as ensuring that turns are wide and gradual. Kevin notes that turns which are too sharp can lead to pressure-killing kinks, especially when hot water starts softening pipe walls.
Additionally, he says, even though installation is generally easier for PEX-based systems, the added number of pipe runs in a manifold design can push costs somewhat higher than they'd be for traditional copper-pipe alternatives. He uses a typical bathroom, with a toilet, sink and tub/shower as an example of the added material and labor a manifold approach can entail.
"It is faster [to install each line]," he says. "But you're running five lines instead of just two."
Chuck Ross is a Brewster, Mass.-based freelance writer who specializes in construction and architecture.
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