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I am sometimes called upon to service a gas water heater, furnace, boiler, range or other gas equipment.

I am sometimes called upon to service a gas water heater, furnace, boiler, range or other gas equipment that appears to be producing less energy than the customer feels is adequate. Some of these calls are unfounded but others are legitimate complaints. After exploring many of the possible conditions that might be causing this problem, we quite often still can't come up with an accurate diagnosis.

There are times that for various reasons the appliance in question may not be utilizing gas at the rate of input for which it was designed. Therefore we must determine if the burner is functioning at its designed rate of consumption or if it is burning at a level less than optimal. This can be accomplished simply, by utilizing the gas meter and a watch with a second hand. To understand how to perform this procedure, the following basic information must be understood by the servicing technician:

1 Natural gas in this region has a heating value of approximately 900 - 1,200  British Thermal Units (BTU) per cubic foot (CF). This means that 1 CF of gas, when completely burned, will produce 1,000 BTUs of energy.

2 Gas appliances are rated by their manufacturers as to how many BTUs of energy they will  produce or CF of gas they will consume for each hour the burner is in operation. This information will be found on the appliance's rating plate and is usually stated as, "INPUT [number) BTU/HR," Knowing that 1 CF of gas can produce 1,000 BTUs, we must be able to assure that we can supply 1 CF of gas for each 1,000 BTUs of rating.

To determine the actual input of gas being consumed by the appliance we can measure or "clock" the actual rate of input to the burner by reading the gas meter and timing the rate of gas consumption by the appliance. The gas meter has various dials that indicate the volume of gas in CF that has passed through it. For this procedure we are only concerned with either the half (. 5) CF dial or the 2 CF dial.

To clock an appliance, perform the following steps in the order listed:

Shut all appliances and gas consuming devices except the one being tested.

Raise the thermostat or heat control setting for the appliance to a point high enough to insure that it will burn continuously without shutting down until you shut it down.

Start the appliance burning.

At the gas meter, accurately count the number of revolutions turned on either the . 5 CF dial or the 2 CF dial for exactly one minute (60 seconds). This will measure the revolutions per minute (RPM) of that dial. For example, the dial may have turned 2 times, or it may have turned 3.5 times, or 5.75 times, or any other reading higher or lower.

Multiply this reading by:

For the .5 CF dial--- RPM X 30 = CF/HR
For the 2 CF dial--- RPM X 120 = CF/HR.

This is the volume of gas in CF/HR, actually being consumed by the appliance being tested.

Compare the number found in step 5 with the BTU input rating of the appliance. If it is less than the manufacturer's listed BTU rating, the burner is not being supplied with the proper volume of gas.

For example:
Let us assume that a boiler rated at 150,000 BTU/HR does not seem to be providing an adequate amount of heat. If we suspect that the input to the boiler is not what the manufacturer designed it to operate at, we have to determine the actual input that is being supplied to the burner.

Following the above procedure, suppose the .5 CF dial in one minute's time has revolved 4 revolutions (4 RPM). When we multiply 4 X 30 = 120. Or if we are observing the 2CF dial, it will have revolved 1 time, 1 X 120 = 120. Therefore, 120 CF/HR is the actual input being supplied to the burner. This is substantially below the 150 CF/HR input required to yield the 150,000 BTUs, the boiler is rated to produce. Knowing this, we must look for the various reasons that may be causing this problem.

Some of the explanations for this may be:

Inadequate gas pressure from the gas supplier.

Obstructions or debris in the gas piping, valves or pressure regulators.

Undersized gas piping.

A defective appliance gas valve.

Clogged or improperly sized burner orifices

The final resolution to the problem will involve a careful, logical process of elimination and a step by step investigation into all of the possible reasons that could cause the problem. It is imperative that when working with gas, all due care and diligence be taken and adherence to all safety precautions be observed in every phase of servicing and troubleshooting. Only persons properly trained to work with gas should attempt to do so.

It may be possible that the gas supplier will have to be called upon to correct the problem if it is found that the reduced input is caused by defects in the supplier's equipment. Whatever the solution to the problem is, determining the rate of gas input is among the first important steps to take for properly troubleshooting gas equipment.


Sylvan Tieger, LMP (Licensed Master Plumber)