Gas line - Max BTU on 60' 3/4" pipe

Discussion in 'Plumbing Building Code' started by auradeus, Jul 10, 2018.

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  1. Jul 10, 2018 #1

    auradeus

    auradeus

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    My plumber has extended a 3/4" black iron gas line that originally supplied just my stove cooktop to a future for a fireplace. The total run is 45 ft of 3/4", reduced to 1/2" after a two separate tees that then feed up about 3 ft to the two fixtures. The stove is only gas for a cooktop (oven is electric - dual fuel stove), and I estimate the cooktop burners max out at 36K BTU if they are all on at the same time (probably a very conservative estimate). The fireplace maxes out at 26K BTU. The plumber seems to think this 3/4 inch supply over 45 feet is plenty to serve the cooktop and the fireplace, please let me know if anyone disagrees.

    My primary question is whether we could continue the run to terminate outside to the deck of my house, extending the run to about 60 feet total, and then provide a supply for a natural gas grill, which would pull at most 100K BTU (probably less). My plumber is having a really hard time figuring out if the supply is sufficient to do this, not sure why.

    Can anyone help? I'm in Massachusetts, which is a little over the top with code compliance, and want to make sure I have my ducks in a row as I need to close up my basement after this job is done, which would make any retro fixes a major hassle.
     
  2. Jul 10, 2018 #2

    havasu

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    How many 45 and 90 degree fittings will you have in the run?
     
  3. Jul 11, 2018 #3

    auradeus

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    Currently (without the extension for the grill) there are four 90 degree fittings (no 45s at all) including the first vertical to horizontal 90 off the 1" supply. There are also two 3/4 x 1/2 x 3/4 tees for the 1/2" reduced run to the fixtures (1/2" runs are less than 3 feet).

    If we extended the run for the gas grill, there would be seven total 90 degree fittings, including the last 90 to bring the run up to the terminated deck fitting that would have a 1/2" reduction on it.

    EDIT: said "(without the extension for the fireplace)" but meant "the grill"
     
    Last edited: Jul 11, 2018
  4. Jul 11, 2018 #4

    havasu

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    I'm not good at crunching numbers, but I know I used 3/4" gas line to run to a small fireplace 40' away. I had 2 90 degree fittings, and I only got a trickle of flame. I increased to 1" pipe, and I had adequate pressure.
     
  5. Jul 11, 2018 #5

    fixitron

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    Referencing NFPA-54, each threaded 90 deg el of 3/4" sked 40 metallic pipe (black iron) is equivalent to 2 feet of pipe. 60' + (2x9)' = 78 ft. of pipe. You don't say whether you have natural gas or propane.
    For natural gas @ 11 inWC, that pipe can carry a maximum of 214,000 BTU/Hr (assuming ~1,000 BTU/Hr per cu.ft. of gas)
    For propane @ 11 inWC, that pipe can carry 212,000 BTU/Hr
    3/4" black iron pipe would be large enough

    For havasu- your problem with a flame is not from using 3/4" pipe (1/2" for a fireplace at 40 ft., assuming no other appliances, would be plenty large enough).
     
  6. Jul 11, 2018 #6

    havasu

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    I apologize. I made an error. I had 1/2" black pipe and it was necessary to increase to 3/4" pipe to allow adequate flow. Sorry, with age ya lose memory!
     
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  7. Jul 11, 2018 #7

    TomFOhio

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    The gas company will have a book that tells how many btu's on a certain size and length of pipe that can be used.
     
  8. Jul 12, 2018 #8

    wood4d

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    you need to give us the pressure from the gas company in your area to do calculations. All the pipe sizing charts are for specific " of water column. In my area 3/4 pipe is not enough for the required btu.
    also you are probably way too high on your grill btus. My two burner weber is only 26k.
     
  9. Jul 12, 2018 #9

    wood4d

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    edit I think the 3/4 is fine for existing stuff. adding a big hunk of btus on the end is the issue
     
  10. Jul 12, 2018 #10

    Diehard

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    In Mass. the nominal service pressure is(very possibly) 6” W.C. (It could be between 5" and 7" W. C. )

    0.5" W.C. pressure drop is typically allowed through the house piping.

    This assumes that the required pressure at the point of use does not exceed 3.5" W.C.

    The Gas Fitter/Plumber should confirm service pressure at the meter and simply look at a gas piping sizing chart for 0.5" W.C. pressure loss, for the loads and total distances(including fitting losses). I suspect you're looking at a minimum of a 1" pipe(from the meter) if you want to run 100 BTU at the gas grill.
     
  11. Jul 12, 2018 #11

    auradeus

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    Thank you all.

    It looks like Massachusetts allowable pressure loss is up to 0.5 WC (CMR 248 Amendment 5). Someone commented that I overestimated my grille BTU, and they were right, even 40K BTU would be conservative. Referencing NFPA 54, conservatively (assuming <2 PSI inlet pressure, I bet my pressure is higher), and revising the total demand to 102K BTU (Cooktop 36K, Gas fireplace 26K, and Grille 40K), the total length would be capped at 100ft. With my estimate of the finished run at around 78 ft (including 9 turns, as someone mentioned, 2 ft per turn), it looks like I'm well within the limits.

    Sound like I'm on the right track?
     
  12. Jul 13, 2018 #12

    Diehard

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    Looks like you should be okay with a total equivalent length of 100 ft and 102k BTU of natural gas.
    What makes you think you have more than 2 PSI available to you(Not that you require it)?
    I know it varies between cities and towns within MA.
     
  13. Jul 13, 2018 #13

    auradeus

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    Less than 2 psi. The most conservative inlet pressure chart in NFPA54 assumes a less than 2 psi pressure. That’s the chart I used to come up with a max length of 100ft
     
  14. Jul 13, 2018 #14

    Diehard

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  15. Jul 13, 2018 #15

    Diehard

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    There is a chart for less than 2 psi because it is a different formula for calculating low pressure gas. And that's the correct chart to use for applications with less than 1/2 psi gas.
    The reason I say less than 1/2 psi gas is because although NFPA 54 allows up to 2 psi gas for residential applications, Mass. only allows 1/2 psi or 14" WC max.

    The only reason I asked the question was you had said, "I bet my pressure is higher".:D
    Now you probably know more than your plumber on this subject.
     
    Last edited: Jul 13, 2018
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  16. Jul 13, 2018 #16

    Diehard

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    Was that drain piping, as shown in your picture, installed by a licensed plumber???
    So this comment ended up in the wrong thread. I was wondering Why it didn't show up the first time. LOL :oops::oops:
     
    Last edited: Jul 13, 2018
  17. Jul 13, 2018 #17

    auradeus

    auradeus

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    Are you responding to the right thread? I didn't post any pics...
     
  18. Jul 13, 2018 #18

    auradeus

    auradeus

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    Haha, I can now understand why my plumber had a hard time figuring this out.

    You're right, I did say that. When my plumber turned the gas back on after he extended the run for the fireplace, he remarked that he was surprised how quickly that the gas reached the stovetop as he bled the system, and chalked it up to "good pressure."

    It is shocking to me that my house only has 1/2 psi of pressure coming in from the regulator, yet that is enough to supply an on demand boiler (separate run), cooktop, and now possibly a gas fireplace and grill. But I suppose not much pressure is needed when working with volatile chemicals...
     
  19. Jul 13, 2018 #19

    Diehard

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    Sorry! You're correct, wrong thread.
     
  20. Jul 14, 2018 #20

    Mr_David

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    Typical Natural gas pressure in a home is about 1/2 psi normally gauged with a hydrometer with a scale reading of inches of water column.

    Gas demand calculation require: input / heating value of gas which is ( BTU/hr ) / ???? BTU/cubicfeet where (???? )the average heating value of your gas supplier can provide.
    with code book example of 1050 btu/cuft. We simplify it by taking a 50,000 btu appliance divide by 1050 = 47.62 cuft/hr

    once you figure out the Cubic foot per hour CFH then you need to make a simple drawing of each appliance an a good rough estimate of distance of piping from meter to each branch line and to the MOST REMOTE OUTLET. attached drawing is an example. No need to show all turns and or fitting. Just distance.


    gas pipe size.png
     
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