Efficient Plumbing Supply Layouts

Home-run Layouts from a Manifold Can Reduce Waiting Time for Hot Water

Bird's eye view

Diameter of the line, distance and speed the water travels affect heat loss

In an older home, water supply pipes are often an archeological puzzle, with a mixture of galvanized pipes, copper tubing, and plastic pipe wandering through joist bays and walls.

In a home with a supply manifold and PEXCross-linked polyethylene. Specialized type of polyethylene plastic that is strengthened by chemical bonds formed in addition to the usual bonds in the polymerization process. PEX is used primarily as tubing for hot- and cold-water distribution and radiant-floor heating. tubing, repairs and changes to the system are easier. Home-run manifold plumbing systems also save both water and energy.

See below for:
ABOUT MANIFOLD SYSTEMS
ABOUT SUB-MANIFOLD SYSTEMS


Key Materials

PEX tubing reduces leak risk

Home-run systems are usually plumbed with PEX tubing, although copper tubing can also be used. Typically a single length of PEX is run from the manifold to the fixture so there are few joints (opportunities for leaks) compared to a rigid-pipe system.


Design Notes

Efficient floor plans make plumbing easier

Keep fixtures as close together as possible. The most efficient approach is to design a “plumbing core” where all bathrooms, kitchens, and other water demands radiate from one chase. This does put limits on the shape and layout of the home, but it will give the best savings of materials, labor, and energy.

Match the plumbing layout to the floor plan. If a house is small enough, a home-run system with one main distribution manifold may be the most resource-efficient installation. In a larger home, it may be more challenging to group all rooms with plumbing around one chase. A sub-manifold layout with more than one cluster of fixtures may make more sense in this case.


Builder Tips

PEX is easier to install

Because PEX is flexible, fewer elbows are required compared to copper, making installation easier.


The Code

Minimum line diameter is 3/8 in.

Manifold plumbing systems are covered in Section 2903 in the 2006 IRCInternational Residential Code. The one- and two-family dwelling model building code copyrighted by the International Code Council. The IRC is meant to be a stand-alone code compatible with the three national building codes—the Building Officials and Code Administrators (BOCA) National code, the Southern Building Code Congress International (SBCCI) code and the International Conference of Building Officials (ICBO) code.. Manifolds and tubing must be sized according to Table 2903.6(1). The minimum size of individual lines is 3/8 inch with two exceptions:
1. Larger lines are required by a fixture manufacturer.
2. When a water heater is supplied at the end of a cold water manifold, the manifold must be one size larger than the water heater feed.
Manifolds can be installed in a vertical or horizontal position (2903.8.3). Individual lines and bundled lines must be supported and secured according to manufacturer instructions and Section 2605 found in General Plumbing Requirements. When a bundle changes direction more than 45° it must be protected with sleeves or wrapping to prevent chafing (2903.8.4).

OTHER CONSIDERATIONS

Hot water pipes may run through cooler parts of the house — a crawl space or joist bay in the basement ceiling, for example. Wrapping the lines with foam insulation reduces energy losses, and gets hot water to its destination faster.

Pipe insulation also reduces condensation on cold water lines during the summer.

GREEN POINTS

LEEDLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. -H EA7 (Energy & Atmosphere) offers 2 points for efficient hot water distribution.

NGBSNational Green Building Standard Based on the NAHB Model Green Home Building Guidelines and passed through ANSI. This standard can be applied to both new homes, remodeling projects, and additions. Under Ch. 8 — Water Efficiency: up to 8 pts. for hot water use reduction based on efficiency hot water distribution system design/layout (801.1)

ABOUT EFFICIENT PLUMBING LAYOUT

Sound planning saves energy

Heat losses increase with the diameter of the line, the distance the water must travel, and inversely with the speed at which the water moves. A large volume of slow-moving water sheds more heat as it travels to its destination than a smaller amount of water moving quickly.

For that reason, trunk-and-branch systems (which require large diameter tubing) are inherently less efficient at retaining heat, especially when hot-water lines are not insulated, than manifold home-run systems.

Heat loss in conventional systems. A 3/4-in. dia. supply line in a trunk-and-branch system holds a lot of water. When a hot-water tap is opened in a bathroom far from the water heater, all the water sitting in the 3/4-in. pipe must flow through the system before any hot water reaches the user.

In a home-run system, the tubing is usually only 3/8 in. or ½ in., so less water is wasted before hot water reaches the faucet.

ABOUT MANIFOLD SYSTEMS

Home-run vs. trunk-and-branch system

In a trunk-and-branch system, the main supply lines, the “trunks,” carry water to the general area where it will be used. Smaller-diameter tubing, the “branch” lines, get water to showerheads, faucets and other points of use. In residential construction, trunks are often ¾-in. dia. and branch lines ½ in.

In a manifold system (also called a "home-run" system), the hot water and cold water supply lines feed a manifold that distributes hot and cold water to each fixture in the house. Each fixture gets a dedicated run of tubing from the manifold.

Manifolds are like main electric panels. Manifolds have separate chambers for hot and cold water. The cold-water chamber is fed from the main water supply line and the hot-water chamber is fed from the water heater, usually with 3/4-in. tubing. Smaller individual lines (3/8 in. or ½ in.) are run from valves on the manifold to each fixture.

Each fixture has its own valve. The manifold is analogous to the breaker box in an electrical system. Just like circuit breakers, the valves on the manifold allows water to individual fixtures to be turned off while leaving the rest of the system unaffected.

Home-run advantages. A home-run system requires more tubing than a conventional trunk-and-branch system because each fixture has its own dedicated water supplies. Still, there are several advantages:

  • Water pressure remains stable to all fixtures when several are used at the same time.
  • Hot water is delivered faster and less water is wasted.
  • Simplified installation means lower costs.
  • Home-run systems work well with open building systems, allowing less invasive, easier remodeling.

ABOUT SUB-MANIFOLD SYSTEMS

Most rooms get their own manifold

Sub-manifold systems are a hybrid between home-run and traditional trunk-and-branch systems. In a sub-manifold system, there may be no main plumbing manifold. Instead, each bathroom, laundry, and kitchen gets its own sub-manifold.

The simplest system won’t save any water over a trunk-and-branch system, but sub-manifolds can be configured to save water and energy.

Multiple points of distribution. In a sub-manifold system, trunk lines run from the water supply and water heater to sub-manifolds located throughout the house. Smaller lines, controlled by valves, supply fixtures downstream.

Design decisions affect system efficiency and the amount of tubing required. Some designs use a sub-manifold to replicate a trunk-and-branch system, while other designs incorporate a sub-manifold into a home-run type system to zone all of the fixtures in a bathroom or laundry room on a single supply.

When to choose. Several situations might call for the use of a sub-manifold system rather than a home-run system:

  • A sub-manifold allows the use of a circulating pump, something you can’t do with a home-run system
  • Sub-manifold systems require less tubing, less drilling, and less time pulling PEXCross-linked polyethylene. Specialized type of polyethylene plastic that is strengthened by chemical bonds formed in addition to the usual bonds in the polymerization process. PEX is used primarily as tubing for hot- and cold-water distribution and radiant-floor heating. through framing than a home-run system
  • In larger houses with long distances between the water heater and fixtures, it may make sense to run a large supply line to a sub-manifold that handles smaller supply lines to the fixtures in one area of the house.

FURTHER RESOURCES

Hot Water Circulation Loops


Image Credits:

  1. Don Mannes/Fine Homebuilding
  2. Krysta S. Doerfler/Fine Homebuilding
  3. Charles Bickford/Fine Homebuilding
  4. Daniel Morrison / Fine Homebuilding
Tags:
2.
Thu, 12/13/2012 - 05:07

Response to Al Shawa
by Martin Holladay, GBA Advisor

Al Shawa,
Q. "What is the best type of PEX pipes to use?"

A. These days, PEX tubing is a fairly generic product. Although several manufacturers vie for the market, I doubt if you will find major quality differences between the different products.

Q. "Which is the best price?"

A. That's a question that can only be answered locally.

Q. "Do I need to insulate PEX pipes?"

A. Yes.


1.
Wed, 12/12/2012 - 22:51

Plumbing
by Al Shawa

What is the best type of PEX pipes to use ?
Which is the best price?
Do I need to insulate PEX pipes?


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