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Too large of natural gas line?

ruffryder Member Posts: 2
edited July 2017 in Gas Heating
Hello all, first time poster, short time reader, lol.

Maybe this is a dumb question, but are there any issues with running a larger than needed gas line? I have a large meter installed at my house, and will be running the gas line for a water heater, furnace, cook top, dryer, and possible outside grill and generator.

I have looked up the tables for the minimum pipe size based on total runs and assuming worst case usage (all on at the same time), but I am curious if there is ever an issue with running larger than needed pipe?

Based on the btu requirements, I was planning on running 1 1/4" pipe from the meter till the first T. Is there any issues running 1 1/2" instead? From all of my searches I haven't seen anything, nor does common sense tell me that it would be an issue.

I would just like some confirmation before I begin the process.

Thanks all!


  • ratio
    ratio Member Posts: 3,553
    The only downside to oversized gas lines is the increased cost (& harder work) as the sizes get larger. There may be permitting & inspection issues, depending on your location, if you're a homeowner as opposed to a license holder.
  • hot_rod
    hot_rod Member Posts: 20,826
    run the sizing numbers carefully if you connect a NG generator, they can cause pressure issues when they kick on.

    Many a mod con experience lock outs when generator installers add a gen system after the line was sized and installed :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EBEBRATT-Ed Member Posts: 14,560
    This is a case where bigger actually is better
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I did not have gas in my house when I wanted to convert from oil to gas heating. The gas company had to install a new gas line from the street all the way to the house. Heavy duty plastic tubing put in with a gizmo called a mole, so they dug a hole in the street and one near where the meter was going to be and basically pushed the tube through the ground. I think that was, perhaps, one inch diameter tubing that has 50 psi gas in it. They converted from plastic to metal in the ground, and hung the regulator and meter from the metal pipe. Just before the meter, there is a regulator that reduces this to (I believe) seven inches water pressure for the house. The run from the meter to the boiler is one-inch and is reduced down to 3/4 inch, runs through a shutoff cock, reduced down to 1/2 inch to the T, and 1/2 inch into the boiler.

    When I had a 12 KW natural gas backup generator installed, the gas company said everything would be fine, but to use 3/4 inch pipe all the way to the generator. The generator company's plumber used 1 1/4 inch pipe because they said it worked better that way. When that came out of the ground, they reduced it to 3/4 inch, ran it through a shutoff valve, and reduced it to 1/2 inch as it entered the generator. It does not seem to annoy my boiler. As far as I know, the cost of the plumbing job for the gas pipe was mainly labor, overhead, profit, and very little for the pipe.
  • ratio
    ratio Member Posts: 3,553
    There's a trend nowadays to size gas lines for maximum pressure drop. It works out on paper, and is cheaper than sizing it by the old tables, but it's bitten me on the you-know-what to many times for me to get on board with it. Size it too large & it'll cost slightly more than it could. Size it slightly small & everything mostly work right. Send like a no-brainer to me.
  • ruffryder
    ruffryder Member Posts: 2
    Thank all for the advice. I was lucky to purchase a used Ridgid 700 threader with dies and the stand for a good price, so it will be easy for me to run most of the pipe in 1.5" rather than going through and doing all of the step downs. My taps off the main trunk will be 1", so all should be well. It will be over sized by a size or two, but will be easier and I won't need so many different dies and stuff.

    Thanks all and happy piping!