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  1. #1
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    Oct 2001
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    I am adding a natural gas appliance at my home and trying to determine if I need a larger capacity meter. My total load will be around 500,000 BTU (500 cubic feet per hour) if everything is on.

    The specs on my meter (Equimeter R415) are listed as:

    415 cfh at 1/2" w.c. diff
    900 cfh at 2" w.c. diff

    I know w.c. stands for water column but how do I know if I have a 1/2" diff or a 2" diff and what exactly is measured by this diff?

    I've tried asking my gas company but they are no help.

  2. #2
    Join Date
    Jan 2005
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    Your existing meter is a Rockwell 415 which is good for 415,000btuh. We calculate our meter requirements based on 75% of the total load, so using this calculation your existing meter would be sufficient for a total load of 500,000btuh. (500,000x75% = 375,000). The differential is the pressure drop across the meter, which in most cases is 1\2" w.c. If your meter has a regulator upstream of it the outlet pressure on a standard residential installation is is approx.7.5"w.c - the .5"w.c. across the meter leaving you with a house line pressure of 7"w.c. Depending on where you are located you may have a higher house line pressure. Here in Alberta you are allowed up to 2psig line pressure inside of a residential one & two family dwelling, but most are 7"w.c.I'm very surprise that your local gas company would not provide you with any meter information>

  3. #3
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    Oct 2001
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    42
    Thanks for your reply. Could you go into a little more detail on the w.c. differential? What causes the w.c. diff to be 0.5" vs 2" and how do you make it 2" so it can supply up to 900 cfh?

    I do have a regulator upstream of the meter if that matters.

    Thanks

  4. #4
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    Jan 2005
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    Did you get that off of the the front rating plate of the meter? I don't have that particular meter in my vehicle so I'm not sure exactly what you are looking at, but if your upstream regulator is reducing the incoming pressure from psig to inches w.c. then all you need to know is that your differential across the meter will be .5"w.c which will allow that specific meter to supply 415,000 btuh capacity max.

  5. #5
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    Jan 2005
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    One other thing to remember is that your existing house line must be of sufficient size to handle any additional loads you are adding to the system. Meter capacity cannot compensate for an undersized house line !

  6. #6
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    Oct 2001
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    42
    Originally posted by blk
    One other thing to remember is that your existing house line must be of sufficient size to handle any additional loads you are adding to the system. Meter capacity cannot compensate for an undersized house line !
    The new appliance is 200,000 BTU and it is connected with 70 feet of 1-1/4" pipe.

    Originally posted by blk
    Did you get that off of the the front rating plate of the meter? I don't have that particular meter in my vehicle so I'm not sure exactly what you are looking at, but if your upstream regulator is reducing the incoming pressure from psig to inches w.c. then all you need to know is that your differential across the meter will be .5"w.c which will allow that specific meter to supply 415,000 btuh capacity max.
    Yes, that is off the rating plate on the meter.

    Am I looking at this the wrong way? Is the rating plate telling me that "you will have this much pressure drop at this much cfh load (0.5" @ 415cfh, 2" @ 900 cfh)? So that I can still run it at higher than 415,000 BTU but that the appliance will recieve less than 7.0" w.c. pressure? And is the 2" wc rating just sort of the accepting max limit since the pressure would be down to 5" or so by then?



    [Edited by jo8243 on 02-20-2006 at 05:28 PM]

  7. #7
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    Jan 2005
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    448

    Talking

    To be perfectly honest with you jo8243, I don't recall seeing two differential ratings on that particular meter so I can't answer your question with any degree of certainly, perhaps someone else on here may be able to help...Mike3 where are you? Getting back to your original post, your existing meter will be adequate for your needs.HTH

  8. #8
    Join Date
    Feb 2004
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    2,479
    Hi
    Just saw your post..I was not able to get a meter capacity chart from my company today..Probably tomorrow..In the mean time I found one from Sierra Pacific.. We set meter for commercial or one appliance only to match or exceed the load...However, with res we use a 60% diversity factor meaning if the total connected load is say 500,000 we would probably set a 310 which will pass around 525 I believe. The meter doesn't need to pass full load because it is assumed that all appl will not be on at the same time.. Of course you must take each situation into account. If it was heating only probably should be close to capacity..
    We set our regulators when new to 7.5"wc and then expect a drift to 7.0" after it has been installed for a while. After that we leave at 7". The "diff" is just as blk explained. The 2" diff is because of the large load being consumed on "that size" meter


    http://www.sierrapacific.com/service...es/GM0030G.pdf

    As you can see from this chart a 425 will pass 620cfh

    [Edited by mike3 on 02-21-2006 at 07:30 PM]

  9. #9
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    Oct 2001
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    42
    Thanks Mike! Great info.

    I'm satisfied now that my meter will be enough. It says the 2" point is 900 cfh. Since I'll only be drawing 500 cfh max that will be fine.

    Out of curiousity though, why can't you just turn the regulator pressure up to 8" or so to overcome the meter loss if it is too high?

    Thanks

  10. #10
    Join Date
    Feb 2004
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    2,479
    Originally posted by jo8243
    Thanks Mike! Great info.

    I'm satisfied now that my meter will be enough. It says the 2" point is 900 cfh. Since I'll only be drawing 500 cfh max that will be fine.

    Out of curiousity though, why can't you just turn the regulator pressure up to 8" or so to overcome the meter loss if it is too high?

    Thanks
    It becomes a billng issue..

  11. #11
    Join Date
    Jan 2005
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    448
    Thanks for the detailed explanation Mike. It should be noted as well that meter capacity and differential loss on the meter rating plates are indicated in cubic ft/air because "air" is the test medium used to calibrate & test natural gas meters , so that rating will be slightly less than the actual natural gas capacity of that same meter..Specific gravity of air being 0 and natural gas being 0.6 . Also meters have a maop( maximum allowable operating pressure)which in the case of the particular meter you have can be either 10psig or 25psig if I'm not mistaken, therefore if you have a greater presure thru the meter other than 7.5"w.c let's say 2psig your meter capacity will also increase. This same meter then becomes what we call a PFM or Pressure Factor Meter which again is a billing issue. Now that you are totally confused......

  12. #12
    Join Date
    Feb 2004
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    2,479
    Originally posted by blk
    Thanks for the detailed explanation Mike. It should be noted as well that meter capacity and differential loss on the meter rating plates are indicated in cubic ft/air because "air" is the test medium used to calibrate & test natural gas meters , so that rating will be slightly less than the actual natural gas capacity of that same meter..Specific gravity of air being 0 and natural gas being 0.6 . Also meters have a maop( maximum allowable operating pressure)which in the case of the particular meter you have can be either 10psig or 25psig if I'm not mistaken, therefore if you have a greater presure thru the meter other than 7.5"w.c let's say 2psig your meter capacity will also increase. This same meter then becomes what we call a PFM or Pressure Factor Meter which again is a billing issue. Now that you are totally confused......
    Nicely stated..I believe our resi meters have maop of 5psig..We don't have any 2# systems around here,although its my understanding parts of our service area do.

  13. #13
    Join Date
    Oct 2001
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    42
    Originally posted by mike3
    Originally posted by jo8243
    Thanks Mike! Great info.

    I'm satisfied now that my meter will be enough. It says the 2" point is 900 cfh. Since I'll only be drawing 500 cfh max that will be fine.

    Out of curiousity though, why can't you just turn the regulator pressure up to 8" or so to overcome the meter loss if it is too high?

    Thanks
    It becomes a billng issue..
    Well how do they keep people from cheating them then? You can access the regulator control if I am not mistaken.

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