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Gas Pipe Question

TeachMeSteam Member Posts: 128

I had a tankless water heater installed.

I believe that there is a gas issue because when the furnace turns on while the shower it on, the water will turn cold. I am assuming that the furnace takes too much of the gas off the main gas line.

The main gas line is 1.25''...then branches out to five 1/2'' lines....one goes to the stove, one goes to the furnace, one goes to the tankless water heater, etc. The tankless water heater requires a 3/4'' line. This is achieved because the 1/2'' line turns into a 3/4'' line.

Given this setup, is there enough pressure to the tankless water heater?


  • lchmb
    lchmb Member Posts: 2,997
    it does

    not achieve it actually. You need to maintain 3/4 from your 1.25" main all the way to the water heater. Have someone check the sizing on all lines to verify the appliances are recieving proper pressure's while running.. 
  • TeachMeSteam
    TeachMeSteam Member Posts: 128
    Thank you

    Thank you for your help.

    Looks like the contractor screwed up big time. Debating whether to sue him but I'll probably just have to eat it and pay for it myself.
  • crash2009
    crash2009 Member Posts: 1,484
    My shower gets cold when the heat comes on

    Just because you had a tankless installed, doesn't mean the contractor should have to upgrade the gas line in your entire house for free.  Would be nice though, if they would at least say something like "By the way, you can't run all these appliances at the same time" 

    I found that out the hard way too.  If you want to figure it out for yourself, and double check your next contractor, go to page 19 and print Table 11  http://www.heatinghelp.com/files/posts/5870/eg_boiler_manual.pdf  This chart will tell you how much natural gas can flow through various sizes and lengths of pipe.  Next, go around to all your gas appliances and write down the btu input.  Divide all the btu inputs by 1000.  Then measure all the lengths and diameters of all the gas lines that go to all the appliances.  You might want to call your gas company and ask "How many btu's per hour will my meter allow?"  Think about any appliances you might add in the future, like maybe a generator or an outside grill?  Here is another shortcut to more information that I found to be helpful when I figured out mine.   http://www.propane-generators.com/natural-gas-chart.htm 
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