Plastic Plumbing Manifold - 5/3/2004 - House Systems Plumbing Septics Wells

Plastic Plumbing Manifold

Control centers for hot and cold water that feed flexible plastic supply lines to individual fixtures

A new method for residential water distribution is gaining acceptance in the home building industry. Manifold plumbing systems are control centers for hot and cold water that feed flexible supply lines to individual fixtures. Plastic manifolds together with flexible plastic piping offer installation-related cost advantages over conventional plumbing systems.

Separate manifolds serve hot and cold water lines. The cold water manifold is fed from the main water supply line and the hot water manifold is fed from the hot water heater. Water pressure in the manifolds is maintained by the incoming service line. A dedicated water supply line feeds each fixture from a port in the manifold.

The thermoplastic manifold is lightweight, corrosion resistant, and easily connected to fixture lines and main service. Manifolds are 1¼ inches in diameter -- larger than most service lines -- to enable adequate water flow to individual fixtures. A continuous built-in reservoir provides equalized water flow and helps maintain constant water pressure in all supply lines. Shutoff valves are built into each port for individual control of lines and of flow to individual fixtures.

Manifold systems can use 3/8-inch supply lines for individual fixtures because fewer fittings are required (hence, less pressure drop occurs in the lines) compared to traditional, rigid 1/2-inch lines. Cross-linked polyethylene (PEX) piping is used because of its resistance to temperature extremes, chemical attack, and creep deformation, and its suitability for hot water use.

	Because of its relatively easy installation, this system can save on labor costs. Its can also save on energy bills by not allowing as much pressure and heat loss.
	Manifolds are corrosion resistant and make service relatively simple. The PEX piping is also a better insulator than copper and not susceptible to rust.
	Because all the connections are at either the manifold or the fixtures, leaking is easily controlled. In addition, cutting off the supply can be done at a central location.

Cost of a manifold plumbing system will vary. One distributor estimated that plumbing manifold systems cost up to thirty percent more than conventional rigid copper piping systems. However, some builders have reported a cost savings of about 10-20%.

Not Applicable

PEX tubing and metal insert fittings are required to comply with excessive temperature and pressure specifications of ASTM of standard F877, "Crosslinked Polyethylene (PEX) Plastic Hot- and Cold-Water Distribution Systems."

Model reMODEL: Philadelphia, Pennsylvania

Oakwood Homes: Green Valley Ranch. Denver, Colorado

Plumbing manifolds are mounted in a convenient, accessible location such as a basement wall or a service closet to allow access for shut off to individual fixtures. The thermoplastic manifold is installed near, but not too close to, the water heater. Minimum clearances of 36-inches (vertical) and 18-inches (horizontal) are needed between a thermoplastic manifold and a water heater. Opposing port manifolds can be mounted conveniently between stud framing.

Copper can be used for the main line into the house, and with slab type foundations copper is sometimes used for underground lines on the first level. Special fittings allow the plastic pipe to be attached to the copper (see photos). The PEX pipe slides over the fittings and a metal collar is crimped to seal the connection. PEX pipe can be used under concrete slabs, however it tends to move around before and during the placement of the concrete. Vanguard has developed a new type of pipe to solve this problem. The pipe, known as PEX/AL/PEX has an aluminum sleeve that allows it to hold its shape while still remaining flexible.

PEX piping can be installed with only two fittings for each line -- one at the manifold and one transition fitting at the fixture. A single length of PEX piping can run directly from a manifold through studs and around obstacles.

The PEX pipe is pulled, much like a wire, from the manifold location to the fixture locations. It should be unrolled using a reel, otherwise it may become kinked. The pipe is secured with clips and then cut.

Design Tip: Builders have found that using open-web floor joists allows greater efficiency for PEX installation, and therefore (if specified) should result in a lower plumbing bid.

Installation Tip: Installers have suggested that a tee-connection be placed on the main supply line upstream of the PEX system. This is so the street line can be flushed prior to running water into the PEX manifold. Often the street line accumulates sand or dirt during construction, The sand will ruin the valves in the manifold. The tee can be routed to a hose-bib or sprinkler system.

Crimping tools may eventually wear out, so it is important to check the crimps with a gauge to ensure they are adequately compressed. A simple gauge is available from the PEX supplier.

Vanguard warrants its manifold for a period of 10 years after the date of installation.

Plumbing manifolds can be installed more quickly than rigid plumbing systems with fewer fittings and without the need for piping tees and elbows. The systems permit several fixtures to be used simultaneously without dramatic pressure or temperature losses. By downsizing supply piping, water velocity is increased and delivery of hot water to fixtures is faster. Heat loss in the piping may be less than a copper system because plastic has better thermal insulating properties. Maintenance is relatively simple with plastic manifolds because valves at the manifold for each fixture line permit individual fixture control, shutoff, and maintenance.