Fuel-Gas Piping Test and Regulator Vent Clearance
A 2,000,000 Btu/h rooftop unit and a 400,000 Btu/h boiler are supplied from a 2-psi natural-gas main. The steel piping is 2-in Schedule 40 for 180 ft, then 1-1/2 in for 25 ft to the boiler. Each appliance has a 2-psi-to-7-in-w.c. regulator. The contractor proposes a pressure test at 20 psig with air, using a 0-30 psi gauge marked in 1-psi increments, holding for 30 minutes. The boiler regulator vent terminates 2 ft from the combustion-air intake and 3 ft below a window. The contractor says the test is stricter than code because it is at 20 psi, and the vent is fine because gas is lighter than air.
1. Evaluate the proposed pressure test: required test pressure, gauge, duration, and precautions.
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For a 2-psi system, the minimum test is 1.5 times the maximum working pressure but not less than 3 psi, so 3 psi is the code minimum; 20 psi is not required and may damage regulators, valves, or appliance components if they are not isolated. The test should be with the regulators removed or isolated, using air or inert gas. The gauge must be accurate and have increments small enough to detect the allowable drop; a 0-30 psi gauge with 1-psi graduations is too coarse. The usual duration is 10 minutes; 30 minutes is acceptable if the AHJ wants a longer hold, but the gauge and temperature effects must be considered. Record the pressure at start and end.
2. Evaluate the gas piping sizing and regulator installation, including the vent.
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The 2-in Schedule 40 main at 2 psi over 180 ft is likely adequate for 2.4 MBH; verify with the gas pipe sizing tables for the allowable drop. The 1-1/2 in section to the 400 MBH boiler is also likely adequate. The regulator vent is not acceptable: it terminates 2 ft from a combustion-air intake and 3 ft below a window. Regulator vents must terminate outdoors, above grade, and at the required distance from openings and intakes (typically at least 3 ft, and not below a window); the vent must be sized, protected from rain/insects, and not obstructed. "Gas is lighter than air" does not excuse the clearance. Provide overpressure protection and a proper vent termination.
3. What records and inspection steps should the AHJ require before approval?
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The AHJ should require approved plans and sizing calculations, regulator listings and vent details, a witnessed pressure test with gauge calibration/serial number, test medium, pressure, duration, and start/end readings, and verification that regulators were isolated. Inspect pipe supports, sediment traps, shutoff valves, appliance connectors, bonding/grounding, and identification. Confirm the regulator vent termination and the combustion-air intake separation. The final approval should be based on the corrected test and vent details, not the contractor's statement that the test is "stricter than code."