Journeyman Plumber ExamGas PipingMedium
A plumber is installing a new natural gas line to a residential clothes dryer. The dryer has an input rating of 22,000 BTUs per hour. The gas meter is located 40 feet from the dryer connection. Using standard pressure (0.5 psig) and 0.5 inches water column pressure drop, what is the minimum nominal pipe size required for this installation, assuming schedule 40 steel pipe?
- A1 inch
- B1/2 inch
- C3/4 inch
- D1 1/4 inch
Show answer & explanationAnswer & explanation
Correct answer: B. 1/2 inch
To determine the minimum pipe size, a gas pipe sizing table (e.g., from NFPA 54/IFGC) is consulted. For a 40-foot length, 22,000 BTU/hr, and a 0.5-inch water column pressure drop, a 1/2-inch pipe is sufficient, as it can deliver up to 26,000 BTU/hr for that length.
Why the other options are wrong
- A. This size is significantly oversized for the appliance and run length, increasing material and labor costs.
- C. This size is larger than necessary, leading to unnecessary material cost without significant performance benefit for this application.
- D. This size is excessively large for the appliance and run length, indicating a miscalculation or misunderstanding of sizing principles.
Gas Pipe Sizing
The process of determining the correct diameter of gas piping to ensure adequate gas flow and pressure to appliances based on BTU/hr demand, pipe length, and allowable pressure drop.
- Ensures sufficient gas supply to appliances.
- Prevents excessive pressure drops.
- Uses sizing tables based on pipe material and gas type.
Memory trick: BTU Length Drop, Size it right, or gas won't ignite!