How to Clock a Gas Meter

It is important to know how to properly read a gas meter and apply that information so that homeowners’ gas-fired appliances receive precisely what they need to operate safely for a long time

How to Clock a Gas Meter

Anthony Pacilla

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You arrive on a job site where a co-worker has installed a new piece of gas-fired equipment and some gas piping. He says, “OK, I have everything else ready to go so go clock the meter.”

You walk outside and look at the gas meter. What dial do you look at? What does the reading even mean? Why is it important? As you stare at the meter and rack your brain as to what exactly you are looking for and why your co-worker yells out, “Well, what is it?”

Now what?

Let's start with the furnace. The furnace your co-worker put in is designed to put out a precise amount of heat that we all refer to as BTUs or, as a gas fitter calls it, the firing rate. Every gas purveyor, equipment manufacturer and codebook related to gas requires you to check the firing rate of any gas-burning piece of equipment and compare and adjust it so that it falls within the manufacturer’s acceptable range of standards. This furnace says 90,000 BTU/h, which means it is supposed to put out 90,000 BTUs per hour. So how does clocking the gas meter tell you what you need to know?

There are a few dials on a gas meter. There are “consumption” dials, which are the dials that count toward the gas bill every month, and there are test dials to help you determine if there is a leak on the house line after the meter or to see the flow of gas through the meter. There are dial sets that may say, 1,000,000-100,000-10,000-1,000, and there’s another set that may read 1/2 FT and 2 FT. The test dials are the latter. It stands for 1/2 a cubic foot or 2 cubic feet (they may vary). 

That said, if every gas appliance in the house is running at the same time, the gas meter will show a whole lot of gas traveling through the meter. Therefore, to determine the gas flow rate for the furnace only, you have to go independently shut off each valve at every gas-fired appliance except the furnace. 

Make sure everything that runs on gas is shut off and go outside to the gas meter, find the test dial, and mark the hands' location with a pencil mark on the glass (on both test dials). Now have your co-worker fire up the furnace, making sure that no other gas appliances are firing in the building. You are going to time how long it takes for one of the dials (whichever one makes sense timing wise once you see them start) to do one full revolution back to your mark. This is assuming that the dial hand is smoothly sweeping around the dial.

If the hand is not sweeping smoothly but instead jerking around, you are going to let it go around a few times (counting how many revolutions it made) and keep track of the time it took to go around a few times. This method involves dividing the amount of time it took by the number of revolutions it made. Don’t concern yourself too much with this. It is rare.

That's it. That's a dial test. Now you need to know what that information means. “Clocking” is just another word for “timing.” 

What do I do with this information?

You need to use this information to calculate how many BTUs the gas furnace was using. This requires a formula. You're going to multiply the flow rate by the heating value and then compare that to the manufacturer’s specifications on the gas-fired unit.

You are trying to figure out how long it takes to get one cubic foot of gas. One cubic foot of gas equals 1,000 BTUs of heat. The furnace is rated for BTUs per hour. There are 3,600 seconds in an hour. 

Let’s assume you used the 1/2 FT test dial and it took 20 seconds for one rotation:

Why it’s important

It is crucial to give the heating unit precisely what it needs to operate the unit safely for the longest period of time. Whether the gas equipment is over or under fired, they both present problems for how safely the unit will operate and how long the unit will run efficiently. The rating plate will tell you the parameters you need to stay within. In this example, we are right on the money. 

Think for a moment how rare it would be to provide the gas lines in your house with all the same exact pressure and expect that consistent pressure and volume to be an exact match for each of the varying firing rates of the gas equipment present in your home. It's near impossible. Since the field of acceptable firing rates varies from unit to unit, an appliance regulator must be installed on every gas-fired appliance and must be tested and adjusted manually until the piece has been fine-tuned.

Say you clocked the meter and it showed that the furnace was overfiring. In that case you’d tell your co-worker that he needs a regulator and that he is overfiring by a specific amount (which could lead to him installing a specific type of regulator). If the furnace was underfiring, you could adjust the orifice or make burner adjustments based off the type of unit.

The actual firing rate on an older piece of equipment can tell a technician a lot about how efficiently the unit is operating for its age and could lead to planned replacement at a time of more convenience for a homeowner.  

About the Author

Anthony Pacilla is a registered master plumber for McVehil Plumbing in Washington, Pennsylvania. He has 23 years' experience in the plumbing and HVAC trades, and has a bachelor’s in business and economics from Thiel College.



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