CSLB C-36 Plumbing ContractorPlanning and EstimatingHard
A plumbing contractor is sizing a gas piping system for a commercial laundry facility. The total demand for natural gas appliances is 350,000 BTU/hr, and the longest pipe run from the meter to the furthest appliance is 150 feet. The available gas pressure is 0.5 psi (14 inches water column). Using a typical sizing table for natural gas, what would be the minimum nominal pipe size required for the main supply line to adequately serve this demand?
- A1 inch
- B1 1/2 inches
- C1 1/4 inches
- D2 inches
Show answer & explanationAnswer & explanation
Correct answer: D. 2 inches
To determine the pipe size, one would refer to a gas piping sizing table (e.g., from UPC or NFPA 54). For 350,000 BTU/hr over 150 feet with 0.5 psi pressure, a 2-inch pipe is typically required. A 1 1/2 inch pipe would likely be undersized for this demand and length, leading to excessive pressure drop.
Why the other options are wrong
- A. 1-inch pipe is far too small for this BTU load and length, resulting in severe pressure drop.
- B. 1 1/2-inch pipe could be borderline in some very specific scenarios, but generally insufficient for this combination of BTU and length, risking pressure drop below acceptable limits.
- C. 1 1/4-inch pipe would also be undersized and unable to deliver the required volume of gas.
Natural Gas Pipe Sizing
The process of determining the appropriate diameter of gas piping based on factors like BTU demand, pipe length, available pressure, and specific gravity of the gas.
- Calculated using sizing tables (e.g., UPC, NFPA 54).
- Factors include total BTU/hr, pipe length, and pressure drop allowance.
- Undersized pipes lead to insufficient appliance operation and potential safety issues.
Memory trick: BTU, length, pressure: the gas pipe size creators.