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Adding multiple large appliance supplies at gas meter

housoft Member Posts: 1
edited July 2021 in Gas Heating
Looking for a little advice on how to best plumb in a couple large devices at the meter. I've already determined that adding a T into an existing supply line in the house plumbing won't meet appliance requirements so now I'm trying to determine the best way to get these appliances natural gas.

To start with, I have the gas company coming to de-couple us from the neighbor, upgrade the main line and the meter to support this work. Supply should not be an issue (we've already done the existing BTU/CFM + New appliance math, resulting in this $5000 upgrade).

I'm adding a 22kW home standby generator and a 250k BTU pool heater. Due to supply demands and distance, both appliances will require a 1-1/4 supply line. The appliances are in very different locations as well.

The generator will get polyethylene trenched down to code depth with about 20ft distance between meter and appliance.

For the pool heater, I'm considering black steel pipe run of roughly 100ft through the crawl space (trenching a polyethylene line will require 200+ ft, running black pipe externally on the structure will be about 165ft).

Question: How does the forum best recommend plumbing these two runs at the meter? I'm assuming I need two Ts to build a manifold of sorts, both runs supplied individually by a T. I assume I cannot run a single 1-1/4 T that then forks again to supply both devices, correct?

Thanks for taking the time!


    EBEBRATT-Ed Member Posts: 12,362
    Yes, come off the meter with whatever size the meter is and blow it up to 1 1/4" right away. then put in your 1 1/4" tees. Normally I would make the manifold larger however are you going to heat the pool while the generator is running?? I doubt it.
  • mattmia2
    mattmia2 Member Posts: 5,999
    So here is the longer answer to your previous question about the tee at the meter. The commercial fuel gas code has tables and formulas for calculating pressure drop through sections of fittings and pipes(vs the one size fits all table in the residential code).

    The truly correct way to do it would be to calculate the pressure drop to each of the outlets of the manifold at the requirements of all of the appliances flowing through that fitting after the meter assuming the pressure at the outlet of the meter specified by the utility.

    You then use that as the starting pressure to calculate the drop in each section to each appliance including the existing piping. If you have more pressure than the ratings plate of the appliance requires then the piping is adequate. It is good to have some margin for errors in your measurement and fitting count.

    Keep in mind you will need a riser designed for this purpose to get the polyethylene above ground.

    I highly recommend you get the code that you are under and read the fuel gas section.
  • Lance
    Lance Member Posts: 217
    Sounds like your adding at least a 1000 cubic feet of demand. The question I have is what pressure are you using in your design? low-pressure? 2PSI? It will determine your pipe size according to distance. If all appliances are homerun to the meter manifold, each can be sized independently. But if you choose a standard branching system it all comes down to additive loads for each section of each run. Master gasfitters are best at designing this. If you choose 2 PSI, each mfg of product will have sizing charts.
    With flex, always use lightning strike type. But the safest pipe against lightning is still black steel. http://csstsafety.com/CSST-lightning.html
  • Tim McElwain
    Tim McElwain Member Posts: 4,518
    One of the things to consider is that the generator load is not one that is needed all the time only when there is a power failure. The utility should help you with that determination. As for the pool it is a seasonal load I assume so that should be less demand on the entire system when it is cold. One of the things I have done with the utility blessing is have them run a separate meter just for the generator and boost the gas pressure for that load.
  • dopey27177
    dopey27177 Member Posts: 873
    Key to all the calculations is the main gas piping must be able to support the complete load of all appliances operating at the same time. That includes the gas main from the utility, the meter and the gas piping from the meter to each TR. The pipe reduction can occur after each T. The gas company can help the licensed plumbing contractor with appropriate pipe sizing for each branch line.

    One must take into account that an aberration can occur where the generator and pool heater may come on at the same time and cause a drop in gas pressure that may cause a shut done of the devices and cause pilot lights to drop out and thereby creating a situation where gas enters the building thru failed pilot light.

    Alan (California Radiant) Forbes
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 3,357
    edited August 2021
    I'm with @EBEBRATT-Ed, i.e. two 1-1/4" lines teed into the manifold at the meter. I would also install ball valves on each line at the meter just in case you ever get a leak in one of the underground supply lines. You could turn off the valve which would isolate the leak and allow you to keep the meter on. I would also install a tee with a plugged 3/4" branch at either end in case you wanted to pressurize and test the line.

    Edit: Your 22 kW generator translates to 75,000 BTU. Using the tables below, you could use a 1" line if the distance to the generator is less than 550' and a 3/4" line if less than 175'.


    Often wrong, never in doubt.
  • realliveplumber
    realliveplumber Member Posts: 62
    edited August 2021
    A Generac 22kw uses 327,000 btu. In some limited, short runs, you can use 1". Most of the time its 1 1/4".
  • A Generac 22kw uses 327,000 btu. In some limited, short runs, you can use 1". Most of the time its 1 1/4".
    I get it now, thanks. 1-1/4" it is.
    Often wrong, never in doubt.
  • mattmia2
    mattmia2 Member Posts: 5,999
    22 kw out, not in.
    Alan (California Radiant) Forbes