Natural gas supply line sizing

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Mike F, Dec 18, 2006.

  1. Mike F

    Mike F New Member

    Messages:
    28
    I am looking to find any information on how to calculate natural gas supply line size for a recently installed grill. Burners total 100,000BTU. Though I have not checked it, I am told that supply pressure is approx. 7"w.c. The run is about 70ft or so. I presently have a 3/4" supply, which is great for 2 burners and the "pro sear", which totals 58,000 BTU. When I ignite the last 3 burners, there is a noticeable drop in gas supply to the already lit burners. I have called my gas supplier, and they won't give me an answer, rather they told me to ask a plumber. I contacted Sureheat, who manufactures the grill, and they feel that the supply is probably adequate. The unit is warrantied, but if a repair tech comes out and finds the supply inadequate I may be responsible for the service call. Is there some table or calculator used to figure pipe diameter given a certain pressure for a given BTU requirement?
  2. Last edited: Dec 18, 2006
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,258
    Location:
    Cave Creek, Arizona
    burners

    You have to calculate the pipe's length using all the dimensions from the meter to the grill, not just the pipe you installed. You mention two burners and the "Pro Sear". Does this also have multiple burners? You say when you turn on the last three burners it cuts down on those already lit, which means you must have at least a total of 5 burners. Where did you connect your gas line to? If that connection was undersized then it will limit the amount of gas available. I assume with the pressure you stated, that this is natural gas, not propane.
  4. Mike F

    Mike F New Member

    Messages:
    28
    There are 5 burners and the "pro sear" which is an infrared burner. Each burner is 14,000 BTU and the infrared is 30,000. According to the chart referred to above, my supply should be adquate, but the feed from the gas meter also supplies the hot water heater, stove and bolier. The grill replaced an existing, but smaller, grill and I simply connected into the existing line. I know for sure that the boiler was off, and probably the stove. The hot water I am not sure. I will attempt to get a hold of a pressure gauge and measure supply side pressure, calculate all BTU useage and see where I stand.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,258
    Location:
    Cave Creek, Arizona
    pressure

    The pressure gauge you need is rather expensive because it measures in ounces rather than pounds.
  6. Randyj

    Randyj Master Plumber

    Messages:
    1,047
    Location:
    Alabama
    Interesting you should mention that. Here's a link that I just put on another thread.
    http://www.rverscorner.com/articles/manometer.html
  7. Mike F

    Mike F New Member

    Messages:
    28
    Great timing Randy!
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