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Tankless Hot Water Heater Gas Supply Question

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  • Tankless Hot Water Heater Gas Supply Question

    Let me start by saying that I understand many of you do not like the tankless hot water heaters. I respect that opinion but have a question about them that I hope you will help me out with. Let me start by saying that I am not a plumber and don't play one on TV. Just a homeowner who does not want to have problems going forward. Thank you in advance for your help.

    Old tank is leaking. Going to replace. Plumber says go Rinnai. I say, lets talk. We chat and he says that he needs to upgrade the gas line to 3/4" from the 1/2". Makes sense, no sweat. Here is the kicker.

    Propane tanlk has 1/2" copper into the ground.
    House has 3/4" black pipe coming out of the ground 8".
    8" line expanded to 1" line for 3"
    90 degree bend into house with 1"
    1" line in attic

    House was built in 75. Tank is surrounding on all 4 sides with concrete. Appears to have 1" line running along and then they tapped off with 1/2" to feed each propane appliance. House has 2 gas LP water heaters, LP range/oven, and LP furnace.

    So plumber says he will tie into the 1" line with 3/4" and all should be fine? That scares me a little since 1/2" at the start seems to be the bottle neck. Now maybe the 1" allows for enough volume since it is exapnded and there is nearly 50' of 1" black pipe in the attic but I still am feeling uneasy about this. There is only one regulator and that is at the house.

    Since the tankless will only be supplying 2 bathrooms and the wife takes long showers I thought that it would be a nice touch. Propane ain't cheap either and if I save 10% a year on my propane bill then that would be $200. It would take 4.5 years to break even on the upcharge.

    Regardless, I think I want this if the plumbers idea works. My question to you guys is this, will it work? I called Rinnai and they said the unit I was told to use needed 8.5"-13.5" water column pressure (?) to run properly. Help me out gents.

    Last edited by jasonswick; 04-02-2010, 04:27 PM.

  • #2
    Re: Tankless Hot Water Heater Gas Supply Question

    You need to tell him the BTU spec on the tankless, and have him work that in the National Fuel Gas Code book to see what you need for a supply.

    You say a $900 savings would break you even on the cost of the tankless. That seems low. The units cost more, you may need gas line work, and you will need new flue piping.


    • #3
      Re: Tankless Hot Water Heater Gas Supply Question

      I will mention that. Yes, the pricing does not include the extra line. His price was for taping into the 1" line in the attic. I am sure it will go up from there! I am getting the unit myself since I trade with the wholesaler on the other side of his business, electrical. He's helping me out on the materials.


      • #4
        Re: Tankless Hot Water Heater Gas Supply Question

        Jason, do you have a regulator near the wall of the house where the LP pipe comes thru the wall? Usually a LP tank has a regulator on the tank then a small supply line to the house then another regulator where the LP pipe usually gets bigger to the "sized" pipe in the house. Gas pipe is sized based on overall length and demand. Also most tankless water heaters require 3/4" hard pipe to the appliance.