Adequate gas supply

Discussion in 'Tankless Water Heater Forum' started by guy48065, Sep 27, 2013.

  1. guy48065

    guy48065 New Member

    Messages:
    111
    Location:
    SE and north MI
    I've been reading up on the gas requirements of a tankless heater and I'd like to know how I can know ahead of time if I'll have high enough flow. I thought meter capacity set the absolute max but now I've read a comment in another thread about possibly "needing a bigger line to the street". I never imagined that could be the case. Isn't the supply before the meter at higher pressure? The gas company recently buried new gas mains up the road serving all the subs near me and it's mighty small pipe.

    On a gas meter where do I find the max flow rating? I hope it's more obvious than an electric meter.
  2. Dana

    Dana In the trades

    Messages:
    2,805
    Location:
    01609
    Most residential meters max out at or under ~450,000 BTU/hr. Some max out as low as ~250 or ~300K. Somewhere on the nameplate there is usually a cubic feet per hour at 1/2" water column pressure difference. Multiply the CFH @ 1/2" W.C. number by 1.02 to convert to KBTU/hr. Sometimes the CFH number is embedded in the model name.

    To go bigger than that would require a different meter, but I'd be surprised if there isn't sufficient capacity on the drop line to the main or the main itself to handle substantially more. They generally size the capacity of the mains in developments for normal residential peaks, and they may deny you a bigger meter & regulator even if the grid capacity can currently handle it rather than set a precedent that could potentially overwhelm the capacity.

    Why are you maxed out- do you have a pool heater or something on it? Or is it a <300 CFH meter?
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,892
    Location:
    New England
    Some areas have quite high pressure up to the meter, some don't. Frictional losses through the pipe can be huge once you drop it after the meter. Every joint, elbow, valve, and the diameter all combine to drop the ultimate flow available to the appliance(s) connected to the line.

    A typical tankless system requires a fair amount of gas, and how it is piped from the meter can make it work or not. Then, your meter itself along with the regulator, must be able to provide for your peak needs. Say you have a gas dryer, stove, furnace, barbeque, and you may already be close to the capacity. The point is, don't take it lightly...if the thing doesn't have adequate gas supply, it won't (always, or never) work right.
  4. guy48065

    guy48065 New Member

    Messages:
    111
    Location:
    SE and north MI
    I'll verify the meter. Pipe won't be an issue. I can do a home run to the meter and it'll be less than 15 feet.

    Nothing is "maxed out"-- I just read these dire warnings that tankless requires industrial feeds and a degree in rocket science to install. Of course that's not true. I just want to cross all the "t's" since a 199K tankless is hungrier than all my appliances combined.
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,892
    Location:
    New England
    If your meter can support the max load, and you follow the installation instructions about max effective length (this includes actual length, diameter, plus any fittings), there should be no performance impact, and the thing will work as designed. Now, whether you'll like it as designed, is a totally different issue altogether! WHen a gas supply system is not setup properly, everything on it can be affected, while individual items, running singly, may work just fine.
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