A traditional plumbing system uses a ¾ inch diameter pipe (or even larger for big homes) that makes a circuit around the house with smaller diameter ½ inch pipes coming off to supply individual fixtures. For hot water supply, this is an extremely inefficient use of water. A larger diameter pipe takes more than twice the amount of hot water to supply a remote fixture than an equivalent ½ inch pipe.
As our homes have become larger with more bathrooms and longer plumbing runs, this makes the problem far greater. Coupled with the inefficient water heating systems that are the standard in most homes, the result is an energy and water equation that is working against the homeowner. Water pipes running in marginally conditioned or unconditioned areas also exacerbate this condition.
All of which leads us to manifold systems: a green building technology that mitigates this by using ½ inch take-offs very close to the hot water supply. The individual ½ inch runs use a lot less water and save quite a bit of energy because the user is not having to clear out a ¾ inch line before hot water reaches the fixtures.
When you add in the water saving nature of PEX tubing, this becomes an even bigger factor. PEX tubing works great with a manifold system, and red and blue colored PEX can be used to signify hot or cold water. PEX tubing can also be bundled as the lines snake through the house. Here are some pictures of a manifold and tubing:
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