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Clocking a natural gas meter.
bob eck
Member Posts: 927
in Gas Heating
What is the proper way to clock a natural gas meter?
0
Comments

Depends on the gas pressure. Correction factors sometimes have to be used. Basically you time it for 1 min get cubic feet x 60=hourly input.0

You can probably get a chart from your Nat gas supplier showing seconds at half foot, 1 foot. 2 foot intervals. Ive had mine in my wallet for years. It's the size of a business card.0

I just googled it and then saved the web site to my phone “work” folder. Simple as pie0

oh my,,,
3600 divided by the seconds it takes for 1 cuft to pass= CFH.
a metering pressure of 2 PSI will pass 12% more gas than measured so for example = 3600/36 x 1.12 = 112 CFH.
no need for the 12% if metering pressure is 7"wc0 
I did not see it mentioned but if it is a dial meter, start your timing on the upstroke of the indicator. Make sure only the one appliance you are clocking is on. Or if need to check total make sure all stay on during the test. This test assumes all gas pressures are normal and steady. Pressure flow problems will make the test results worth less.0

Look for the smallest test dial on the meter. Get a stop watch. Get the single piece of equipment you want to clock running. Everything else should be shut off, don't worry about pilots on other equipment. If for instance the test dial you are using is the 1/2 foot dial let it make two rotations (makes the math easier) It becomes the same as a 1 foot dial. So lets say it took 20 seconds to make two rotations of the half foot dial. You divide 20 into 3600 (number of seconds in and hour). In this case 20 divided into 3600 is 180, what is 180 it is 180 cubic feet to then find BTU's multiply 180 times the Heat Value of a cubic foot of gas in your area or if you don't know use 1,000 which means the equipment you clocked is burning 180,000 BTU's per hour. This should closely match what is on the rating plate of the equipment listed as INPUT.
There are charts and tables for all of this in NFPA 54 National Fuel Gas Code. There is also a procedure for altitudes in NFPA 54.1 
If you are interested I can mail you a procedure by postal mail. Contact me with your address by my email [email protected] There will be a slight charge for postage.0

There are several user friendly free apps available, go to google play, and do a search...0

I don't know of some of these comments were directed to me or the OP, but my question is a little more specific than clocking a meter in general. I have, several times in the past, wanted to clock a roots meter that is metering gas at say 10#. From there, the gas goes through a regulator to drop it down to say 14", & then to the appliance. I gather that 1 CCF through the meter at 10# means somewhat more than 1 CCF at 14". My years of Ideal Gas Laws are far behind me, and I can't seem to find anything on the internets that's generic enough that I can plug in the inlet pressure & get an adjustment factor, like ch4man noted WRT 2# above.0

i cant speak for any correction factor other than 2 PSI gas being 12% more than at 7"wc. i believe 14"wc gas through the meter requires a 2% increase.
sorry, cant help on clocking a roots meter @ 10 PSI.
for those who have trouble with these correction factors, most gas meters are only temperature compensated, some pressure compensated. some both.
remember a 80 CUFT nitrogen tank is what 18" tall by 6"wide or so. maybe 1 cubic foot in total area on the outside yet hold 80 cubic feet. this helps explain the need for the correction factor
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sorry, i may have been rambling on the last post...
@ratio, what piece of equipment have you been trying to clock a meter that requires a roots type meter at 10 PSI? that has to have a huge input. typically of such large equipment your better off tuning and checking performance by measuring output with a combustion analyzer.0 
If I recall correctly, most natural gas is sold on a "standard" cubic foot basis, that is 1 cubic foot at 60 deg. F and 1 atmosphere (0 psig or 14.73 psi absolute). Most gas meters that are used for commerce are corrected for temperatures and pressures other than "standard" conditions. So for billing meters, 1 CF on the dial is one standard CF. If the meter is truly not corrected for temperature and pressure then the gas laws apply: more gas in a cubic foot at higher pressure and less gas in a cubic foot at higher temperatures, but you must use absolute pressure and temperature (deg Kelvin) for the comparison. So in absolute units 1 standard cubic foot at 60 deg F and 1 atmosphere is at 288.7 deg K and 14.73 psia (407.9 inches water column). So for example if you are measuring at 80 deg F then the volume at 80 deg F (which is 288.7 + 80 = 368.7 deg K) is 288.7 divided by 368.7 or 0.783 (78.3%) of a standard cubic foot. If you are measuring on an uncorrected meter at 7" w.c. (414.9 inches absolute) then you have 414.9" divided by 407.9" = 1.017 or 1.7% more than 1 standard cubic foot. If you are measuring gas on an uncorrected meter at 10 psig (really 24.73 psia) then you have 24.73 divided by 14.73 or 1.679 or 67.9% more than 1 standard cubic foot. It's complicated and that is why most meters used in commerce are corrected for temperature and pressure or at least the billing statement is corrected for temperature and pressure AND the actual btu value of that particular gas being delivered.
So the correction for both pressure and temperature is basically: Correction factor for temperature = 288.7 deg K divided by your measured temperature plus 288.7. The correction for pressure is your measured gage pressure plus 14.73 divided by 14.73.
...I think I got that right, but it's been a while since chemistry and physics classes.1 
@Gary Smith, thanks, that was about what I was wanting to know. I know that most meters are temp compensated, I've occasionally seen meters with two registrations, one marked temp compensated & one not! I'll look and see if they say pressure compensated too, that'll make things a lot easier.
@ch4man, that one was decent sized. IIRC 500k at low fire, 4:1 turndown, ≈ 2,000k. I was adjusting it via combustion analyzer/ΔT, I was just looking for verification. You can't know too much about things, especially burning that much gas.
<rant>Had a makeup air unit, 3,800k BTUh. The plumber piped it in 1" from the regulator to the unit, about 25' equivalent length, because "it'll be fine and anyway thats what the unit had". <sigh> And people wonder why I'm against sizing gas lines for greatest possible pressure drop.</rant>
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