Journeyman Plumber ExamGas PipingHard
A plumber is installing a gas-fired commercial boiler in a building. The boiler has an input rating of 1,200,000 BTUs per hour. The gas pressure at the meter is 2 psig. The total length of the gas piping run from the meter to the boiler is 120 feet, including equivalent lengths for fittings. Using a 1.0 inch water column pressure drop, what is the minimum nominal pipe size required for this installation, assuming Schedule 40 steel pipe?
- A2 1/2 inches
- B3 inches
- C2 inches
- D4 inches
Show answer & explanationAnswer & explanation
Correct answer: B. 3 inches
For high-pressure, high-BTU systems, specialized sizing tables (e.g., NFPA 54/IFGC Table 402.4(3) for 2.0 psig, 1.0 IWC drop) are used. For a 120-foot length and 1,200,000 BTU/hr, a 2 1/2-inch pipe can deliver approximately 1,170,000 BTU/hr, which is insufficient. A 3-inch pipe can deliver approximately 2,210,000 BTU/hr, which is sufficient.
Why the other options are wrong
- A. A 2 1/2-inch pipe is insufficient, as it can only deliver up to 1,170,000 BTU/hr, falling short of the required 1,200,000 BTU/hr.
- C. A 2-inch pipe is significantly undersized for this demand, leading to severe pressure drops and appliance malfunction.
- D. A 4-inch pipe is excessively oversized, leading to significant unnecessary material and installation costs.
High-Pressure Gas Pipe Sizing
Determining pipe size for systems operating at higher gas pressures (e.g., 2 psig) and very large BTU demands, often in commercial or industrial settings.
- Uses specific high-pressure sizing tables.
- BTU capacities are significantly higher than low-pressure systems.
- Accuracy is crucial for safety and performance.
Memory trick: Big Boiler, High Pressure, Long Run: Table's the Answer, No Guessing, Son!