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Natural Gas pipe sizing

tcarlin | Posted in Construction Techniques on March 20, 2009 08:15am

i used this website
http://www.propane-generators.com/natural-gas-chart.htm

and my tauton code check which has the same charts to try and calculate the sizing of my ng pipes for a remodel.

these are my appliances
furnace – 100,000
tankless water heater – 140,000
dryer – 35,000 (est)
range – 65,000 (est)

i measured the developed length at 72ft so i used the charts at 80ft. and had a couple questions about my results. using the water heater as an example it has a 3/4 fitting on it but the calculations say run a 1″ pipe to it. where do i do the reducing? just before the appliance? also the main line came out at 1-1/4″. the meters as is look like they enter (house side) at 1″ is it okay to go from the existing 1″ up to 1-1/4″ or is that going to be pointless. i understand from researching on here that the pressure on the street side is much higher and that the meter brings it down to the house level. i called my local utility to inquire about what the meter pressure is and the woman said quote: the meter adjusts to the houses needs but its typically between 1/4 to 2 lbs. i do not really know what that means but i thought i would add it if helps.
any advice as to if i am on the right path would be greatly appreciated.

and finally i was talking with a friend who told me that i should go to this hvac supplier near by and get certified to install the flex yellow gas line. said it only costs about $20 and takes about an hour and then i can buy the product from them. does anyone know if that sounds legit and also how using the flex line as opposed to black pipe affects calculations.
thanks

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  1. plumbbill | Mar 20, 2009 10:20pm | #1

    It's normal to have a larger diameter run to the fixture than the size of the fixture inlet.

    Reducing that should be done after the isolation valve (no bushings).

    Also normal to have larger pipe than what the meter outlet is.

    To save my fingers from a lot of typing here is a link to Gastite¯ (CSST) sizing charts.

    http://www.gastite.com/page.php?pg=sc_natural_gas&idlink=link6

     

    1. tcarlin | Mar 22, 2009 12:27am | #3

      plumbbill thanks for the response. a couple follow ups. what do you mean by Reducing that should be done after the isolation valve (no bushings).take a standard water heater hook up. the pipe comes down from the ceiling, has a shut off valve, has a bushing, then a T. the T branches over to the water heater, and the downward piece continues a few inches and is capped to collect moisture. my question is where in this do i go from a 3/4 to 1/2 pipe or 1 to 3/4 as some of my appliances seem to need.also if i go with csst flex pipe instead is there no need for this moisture collection point like with the black pipe? and if i use a black pipe run down the center of my basement and branch off with the csst flex pipe should i calculate with csst charts or black pipe?thanksAlso normal to have larger pipe than what the meter outlet is.To save my fingers from a lot of typing here is a link to Gastite¯ (CSST) sizing charts.http://www.gastite.com/page.php?pg=sc_natural_gas&idlink=link6

      1. plumbbill | Mar 22, 2009 03:32am | #4

        Most common way I have seen & done a WH hook-up with the pipe coming down from the ceiling is......

        Pipe comes down to a tee, out the bottom is a drip leg with cap.

        From the branch of the tee would be a nipple then a valve, nipple then reducing coupling to a flexible gas connector.

        I'm not sure of any jurisdiction that allows bushings on gas lines.

        Most gas ball valves are restrictive, except ButterBall¯ valves, so I like to keep them the same as the line size & reduce after.

        Drip legs are common practice with most systems, but more places are not requiring them as much as they used to.

        The drip leg catches moisture from the service, not what the building is piped in for the most part.

        Running an iron pipe main with csst branches is how we do our hirise residential units. Iron piped is sized as if the whole system would be IPS, csst branches are calculated from their specs.

         

        1. tcarlin | Mar 27, 2009 12:25am | #5

          i took the gastite certification class today. and in their example of using the longest run method for calculating sizing they went like this. main line goes down the center and branches off to appliances. the main line and the last branch to the furthest appliance is 70ft. so they used that distance in the charts. (they did not include the previous branches to other appliances in the length). i was wondering if this is the correct way to do this. when did my first attempt of calculations i was adding in all the branch lines. so their method would lower my overall distance and lower my sizing. also. for example their first appliance was 20 ft down the main line and 10 ft on a branch. so the main is sized to the longest (70) but the branch piece is sized to itself (30) hopefully that makes sense. i was wondering if this is a proper method. thanks for all your help.

          1. plumbbill | Mar 27, 2009 02:17pm | #6

            Yes, that is correct.

            For sizing the main the length is the farthest appliance without including the length of every branch.

             

  2. User avater
    BillHartmann | Mar 21, 2009 02:20am | #2

    There are 2 common ways that NG is done in the house.

    In one they regulate the pressure at the meter to 2 psi. Then at each appliance there is another regulator to drop the pressure to the appliance.

    The other system uses low pressure, I think it is about 10" water column, from the meter.

    I think that the sizing that you show is for the low pressure system.

    It sounds like you might have a 2 psi system. But they could have been talking about the incoming pressure from the main.

    If you have a 2 psi system then you can use lots smaller piping.

    .
    William the Geezer, the sequel to Billy the Kid - Shoe

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