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 heat. There are 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 than the one you are clocking. Even shut off pilot lights, or they can mess with your reading.
#2 – Ensure 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 number of seconds in an hr, so if it's a 1/2 cu/ft dial, it would be 1,800.
#7 – Divide that number by the number of seconds it took. So, let's say it took 22 seconds. That would be 1,800 / 22 = 81.82.
#8 – Multiply that number 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/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 BTUs, you would multiply for the AFUE efficiency. In this case, if it were an 80% furnace, the input is 81,820 BTU/hr, and the output would be 65,456.

Pretty cool, huh?

—Bryan

Related Tech Tips

The "Approach" Method of Charging and Condenser Efficiency
We have been discussing many methods for checking a refrigerant charge without connecting gauges over the last few months. This got me thinking about the “approach” method of charging that many Lennox systems require. The approach is simply how many degrees warmer the liquid line leaving the condenser is than the air entering the condenser. […]
Read more
Density of Air & Water Part 2
Here is part 2 from Michael Housh from Housh Home Energy in Ohio. Thanks, Michael! This is part two in a series on a deeper look into the sensible heat rate equations. You can find the first article here HERE if you missed it. This article will dive deeper into the density of “standard air” […]
Read more
Key Soft Skills for Technicians
  As with most other trades, HVAC/R technicians need to have a solid set of hard skills to make it in the industry. Whether we pick up those hard skills by working on cars as teenagers, learning them in a trade school, or acquiring them on the job, we’ll have to rely on our hard […]
Read more

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

Leave a Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.

loading

To continue you need to agree to our terms.

The HVAC School site, podcast and daily tech tips
Made possible by Generous support from