1. Turn off gas supply to all appliances other than gas-fired boiler.
2. Note the rated manifold gas pressure listed on the boiler’s rating label.
3. Connect Manometer to manifold pressure tapping on Gas Valve (Figure F-1). to verifying input.
4. Light main burners by adjusting thermostat to highest setting.
5. If required, adjust gas manifold pressure to the rated setting by turning the gas valves adjustment screw clockwise to decrease manifold pressure or counterclockwise to increase manifold pressure (Figure F-2). Several turns may be required.
6. On models using more than one gas valve, turn off the gas valve not having pilot control and first adjust the gas valve with pilot control. Then, turn on both gas valves and adjust the gas valve without pilot control.
7. Clock gas meter for at least two (2) revolutions of the dial typically labeled ½ or 1 cubic foot per revolution on a residential gas meter.
8. Determine gas flow rate in Cubic Feet per Hour based on elapsed time for two revolutions. (Example: 70 Seconds for (2) Revolutions = 102.8 Cu. Ft.
9. When the clocked time falls between two table values (Table F-1), add the table values shown above and below your clocked reading and divide by 2 (Example:  68 Seconds for (2) Revolutions = (110.7+102.8) /2 = 106.7 Cu. Ft./Hr.).
10.Obtain gas-heating value (Btu per cubic (foot) from gas supplier or use nominal value of 1000 Btu per cubic foot.
11. Multiply gas flow rate by gas heating value. (Example: 70 Seconds for (2) Revolutions = 120.8 Cu. Ft./Hr. X 1027 Btu/Cu. Ft. = 124,061 Btu/ Hr.
12.Compare measured input rate to input rate stated on rating label. DO NOT EXCEED the boiler’s rated gas input.
13. If input is too high, reduce input rate by decreasing manifold pressure.