Pressure drop with tankless water heater

Discussion in 'Tankless Water Heater Forum' started by hlalicker, May 1, 2009.

  1. Reach4

    Reach4 Well-Known Member

    Sep 25, 2013
    It would be very unusual for the water for your yard sprinklers to be running through your tankless water heater. Look for some other cause of your flow loss. Is there a cartridge water filter, for example?
  2. Tim Beck

    Tim Beck New Member

    Aug 6, 2019
    Middlebury, IN
    Regarding the issue stated earlier about excessive pressure drop in the gas line;
    Nominal size of gas pipe is only half the battle. Simply ensuring that a water heater is supplied by 1" black pipe may not be sufficient. The longer a run of pipe is, the less it can flow. I don't recall the specifics, but black pipe will only flow so many cubic feet per hour of gas per foot of length for each diameter pipe.
    For example, and these aren't factual numbers -- just references to demonstrate what I'm explaining -- 20 feet of 1" black pipe may supply 325 cubic feet per hour of gas, while 30 feet of 1" black pipe might only supply 250 cubic feet per hour. The longer the run, the more restricted the flow of gas.

    The btu demand of your water heater (and all gas appliances) must be converted into cubic feet per hour, and your gas lines must be sized accordingly. The further away from the gas regulator you are supplying gas, the larger the size of the gas pipe is required to be.
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