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  • Installing a tankless, do I need a bigger meter?

    I've been lurking the forums for some time now and I have a question that I can't seem to find the answer to buy searching previous posts so I hope some of the plumbing masters on the forum can help.

    After a lot of research I've decided to go the tankless route with a Rinnai 94Lsi tankless water heater. Because the unit will be installed 30ft from where the gas line comes in from the meter I know a separate gas line will have to be run the full 30ft from a split where the gas line comes in to the house to the water heater. On page 20 of the installation manual it shows how to calculate the size of gas line to use by calculating the gas input BTU/hr of the tankless water heater (190,000) and adding the additional appliances Boiler (140,000) Dryer that I am guessing is (22,000) and dividing by the heating value for natural gas "in my area". I did find in a couple of sources that the heating value of natural gas is around 1000 so adding up all the appliance gas inputs and dividing by the heat value gives me 352,000 / 1000 = 352 cu/ft hr

    However my question has to do with the gas pressure, in the manual the chart that says what pipe size should be used shows the calculation at less than 2psi (55 inches W.C.). My meter says 275 cu/ft hr and 5psi. The initial plan was to T-off from the 1" line coming into the house and increase the size to 1 1/4" to run the 30ft to the water heater. Now having seen the cu/ft hr on the meter and the higher 5psi do I need to call the gas company and request a larger meter? and could I be able to use 1" gas line instead of 1 1/4"?

  • #2
    Re: Installing a tankless, do I need a bigger meter?

    Originally posted by SleepnZJ View Post
    I've been lurking the forums for some time now and I have a question that I can't seem to find the answer to buy searching previous posts so I hope some of the plumbing masters on the forum can help.
    Call an authurized Rinnai dealer in your area. They will be able to tell you what you need.
    BTW, you just opened a big can of worms here. There are many, many, post here on tankless water heaters. Good luck getting someone to tell you what size gas line you need, site unseen.

    After a lot of research I've decided to go the tankless route with a Rinnai 94Lsi tankless water heater. Because the unit will be installed 30ft from where the gas line comes in from the meter I know a separate gas line will have to be run the full 30ft from a split where the gas line comes in to the house to the water heater. On page 20 of the installation manual it shows how to calculate the size of gas line to use by calculating the gas input BTU/hr of the tankless water heater (190,000) and adding the additional appliances Boiler (140,000) Dryer that I am guessing is (22,000) and dividing by the heating value for natural gas "in my area". I did find in a couple of sources that the heating value of natural gas is around 1000 so adding up all the appliance gas inputs and dividing by the heat value gives me 352,000 / 1000 = 352 cu/ft hr

    However my question has to do with the gas pressure, in the manual the chart that says what pipe size should be used shows the calculation at less than 2psi (55 inches W.C.). My meter says 275 cu/ft hr and 5psi. The initial plan was to T-off from the 1" line coming into the house and increase the size to 1 1/4" to run the 30ft to the water heater. Now having seen the cu/ft hr on the meter and the higher 5psi do I need to call the gas company and request a larger meter? and could I be able to use 1" gas line instead of 1 1/4"?
    Call an authurized Rinnai dealer in your area. They will be able to tell you what you need.
    BTW, you just opened a big can of worms here. There are many, many, post here on tankless water heaters. Good luck getting someone to tell you what size gas line you need, site unseen

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    • #3
      Re: Installing a tankless, do I need a bigger meter?

      aaahhhh, did you call the gas co with your info? breid.............

      Comment


      • #4
        Re: Installing a tankless, do I need a bigger meter?

        Im going to take it easy on you

        Plumbertim said it best! "Call an authurized Rinnai dealer"

        Or maybe you should call the gas company?!?

        Better yet, call an Authurized Rinnai installer to do the job, like my self

        Best of luck to you!

        Comment


        • #5
          Re: Installing a tankless, do I need a bigger meter?

          Calculating gas loads is something plumbing contractors do on a daily basis. Hire one!
          Last edited by Plumbus; 09-11-2009, 07:19 AM.

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