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Dimensioning a house's main-pipe

  1. Sep 29, 2006 #1
    When dimensioning pipes for tap-water I add up the capacity of each water-point. My question is, should I also add the capacity for hot water? Let's say that I have 10 fossets, each of which can deliver 0,2 l/s of either hot or cold water or a combination. When determining the size of the house's main pipe, should I then only be concerned about the amount of cold water, since a fosses can't deliver 0,2 l/s of both hot and cold water at the same time?
  2. jcsd
  3. Sep 29, 2006 #2


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    Science Advisor
    Gold Member

    Go buy yourself a book on plumbing. They have guidlines in there that make it much easier. They size different things in I believe what is called 'fixture units'. Each sink, shower, toilet, etc. will be rated at a certain fixture unit. It takes a certain size pipe to carry the water for a given number of fixture units. It is very seldom the main pipe in a residence is bigger than 3/4 inch ID. Also, consider than not all fixtures will be used at the same time. The same logic applies in electrical services. Add the current from each individual breaker in a breaker panel and you will find it exceeds the current of the main breaker. Not everything is used all at once.
  4. Sep 29, 2006 #3


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    Staff: Mentor

    The book you probably want is the BOCA plumbing code. It gives guidelines for that. You don't, for example, just add up all your usage points because they won't all be on at the same time.

    However, to size the incoming service, you do need to consider both the hot and cold water usage because the diversified numbers will be lower than the actual capacities. Ie. [made-up numbers] if you have 10 fixtures at .2 l/s, you may have a diversified load of .5 l/s each for hot and cold water for a total of 1 l/s for the incoming service.

    ....and everything Averagesupernova said is correct.
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