Clocking Gas Meter: Measuring BTU of Natural Gas Fired Heating Equipment

Activate the unit being tested, making certain no other gas fired appliance is operating.



Clock the amount of time it takes for the smallest dial to make one complete revolution.



Using a natural gas meter timing chart (or Table XIII in the National Fuel Gas Code Book, NFPA-54, 1996), cross reference the time and appropriate dial size to determine the BTU input.



Check and compare the calculated input with the input rating on the heating unit data plate.

If the unit is under-fired or over-fired by more than 10%, check the gas pressure to the unit with a fluid filled manometer and adjust as necessary.



(For example, the unit being tested takes 29 seconds for the ½ cubic foot dial to make one complete revolution. Using the chart, this translates to 62 cubic feet per hour. Based upon the assumption that one cubic foot of natural gas has 1,000 BTU’s (Check with your local utility for actual BTU content), the calculated input is 62,000 BTU’s per hour

The reality of using this method to determine actual Btu input is that occasionally gas meters have been found to not be accurately measuring the quantity of gas passing through the meter. Additionally, often meters are not located in close proximity to the boiler room which increases the amount of time and effort required to perform this procedure.

Another method of verifying proper burner input is simply by performing a combustion test and determining that the readings are within the acceptable ranges specified by the manufacturer. If they are, the heating system is operating as designed.