Clocking a Gas Meter (It’s not that hard)

I've heard a lot made of clocking gas meters over the years and honestly, in Florida there isn't too much call for for heat and even fewer furnaces.

I was pleasantly surprised when I found out how easy it actually is. Here is how you do it, step by step.

#1 – Make sure all gas appliances are off other that the one you are clocking. Even shut off pilot lights or it can mess with your reading.
#2 – Make sure the appliance you are checking is running at high fire (max output)
#3 – Get a stopwatch (your phone has one)
#4 – Watch the smallest unit dial on the gas meter, it will often be 1/2 cubic ft
#5 – Time how long that dial takes to make one full revolution with the stopwatch
#6 – Multiply the dial size by 3600 (3600 is the # of seconds in an hr) so if it's a 1/2 cu/ft dial it would be 1,800
#7 – divide that # by the # of seconds it took. So lets say it took 22 seconds that would be 1,800 / 22 = 81.82
#8 – Multiply that # by the BTU heat content of 1 Cu/Ft of gas provided by the utility. If it is 1,000 (which is common for NG) the total BTU per hr would be 81,820

The complete formula is Cubic Feet per Hour (CFH) = (3600 x Dial Size) / Time (seconds)

Then to get the ACTUAL device output in BTU's you would multiply for the AFUE efficiency. In this case if it was an 80% furnace the input is 81,820 btu/hr and the output would be 65,456

Pretty cool huh?

–Bryan

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One response to “Clocking a Gas Meter (It’s not that hard)”

  1. Hey Bryan,

    I recently started a refrigeration apprenticeship in september. You were one of the people that inspired me to pursue this career path.

    I live in Abbotsford BC, Canada and I mainly service high rise residential and small commercial equipment. I am also a journeyman plumber and I have my A ticket in Gas fitting.

    I read your blog regarding clocking a gas meter and I thought you might need to add a caveat because your formula will only apply to a 1/2 psi gas meters or lower. In the Vancouver region, were I live, it is common to have 2 psi gas meters on single family homes.

    Once you go above a 14″ wc meter pressure you need to apply a pressure correction factor: (actual barometric pressure + meter pressure)÷(standard barometric pressure 14.73 psia)
    And a temperature correction factor:
    (Actual temperature: 460°F + dry bulb temperature) ÷ (standard temperature: 460°F + 60°F)

    If somebody tries to apply your formula to a high pressure gas meter they may wonder why its so under fired.

    Anyways, I really appreciate all the podcasts you have been putting out.

    Thank you,
    David

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