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Upgrading gas lines for new Rinnai rsc199ip tankless

I am installing a new Rinnai rsc199ip tankless heater.

Currently, the house has two gas appliances and is fed by all 1/2 pipe. From the tank to the 2nd stage is black schedule 40 1/2"... then the same stuff runs into the house. From there it branches to Home Flex csst 1/2" to feed the stove and dryer.

Attached is a chart showing the proposed run.

I'm looking for insights on how to size the new lines. I'm sure I need to upgrade the 1/2" line from the tank and get a new 2nd stage regulator (it is from 1994!).

Your thoughts on sizing for each stage of the run?


    JUGHNE Member Posts: 11,075
    What PSI does your 2nd stage reg provide to the house piping?

    If it is 2 PSI then each appliance would have it's own regulator to drop the 2 PSI down to 11-13" WC.

    IMO, 1/2" is plenty for the 10 PSI between the regulators. I used to run 3/8" OD copper UG quite a distance from tank reg to house reg.
    EBEBRATT-Ed Member Posts: 15,622
    If you have 10psi from the tank regulator to the house regulator and 2psi from the house regulator to each appliance, then 1/2" inch pipe is good for everything including the new water heater
  • GGross
    GGross Member Posts: 1,070
    I would add that many modern gas appliances need a decent volume of gas immediately at ignition, if each appliance has its own regulator you may have issues if the gas pipe is only a short run from the appliance reg to the appliance. Many manufacturers I have spoken with have recommended at least 10' , though I have had several experiences where we needed a bit more than that.