Should I run a 2nd 1-inch gas line from meter for 200K BTU tankless?

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Old 11-29-10, 12:59 PM
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Should I run a 2nd 1-inch gas line from meter for 200K BTU tankless?

I am confused because I had four plumbers come out - and two of them said I should T from the gas meter with a new 1-inch gas pipe to feed the 200K BTU Rinnai that I will install.. and two plumbers said that I could instead just T from the existing 1 inch main that runs right above the water heater closet and that will be plenty enough. None of them bothered to do any kind of load calc, they were just going based on eyeballing the size of the 3,000 sq ft house. The tankless water heater is the first appliance after the meter if I tap into the existing 1 inch line.

The gas appliances are:

- Rinnai tankless 200K BTU
- Furnace one 80K BTU
- Furnace two 100K BTU
- Gas range 15K BTU
- Gas dryer 10K BTU

The 100K BTU furnace on the opposite end of the house is the furthest tapping from the 1 inch line, almost 100 feet from the meter. The tankless unit would be first in sequence about 20 feet from the meter.

What would happen if I don't have enough pipe capacity when the tankless turns on? Then the 100K BTU furnace would starve for gas.. what would it do? Maybe this would happen only rarely? I am not sure if I should make the walls and attic more of a tangle obstacle course with more pipes if what I have is enough. hmmm..
 
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Old 11-30-10, 10:28 AM
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Yes, you need to run a new pipe from the meter. The two plumbers that told you that the existing pipe is sufficient haven't got a clue.

With your existing pipe being only one-inch AND more than 100 feet long (allowing for any elbows in the piping) you are maxxed out as far as capacity.

Check these links.

http://www.tanklesswaterheaters.com/sizingtable.html

http://www.ecodes.biz/ecodes_support/Free_Resources/Oregon/08_Residential/PDFs/Appendix%20A_Sizing%20and%20Capacities%20of%20Gas%20Piping.pdf

http://www.engineeringtoolbox.com/natural-gas-pipe-sizing-d_826.html

http://www.propane-generators.com/natural-gas-chart.htm

http://home.mchsi.com/~gweidner/pipe-sizing-chart-ng.pdf
 
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Old 11-30-10, 07:17 PM
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Good advice Furd. I will go ahead and get another home run installed to the meter. I suspected that the existing line wasn't enough. It is interesting, I am always coming across licensed contractors whether it be plumbers, electricians, whatever trade, who like to take shortcuts. The more I perform DIY projects, the more I realize how many shortcuts the contractors are taking to get things done faster rather than correctly.
 
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