CSLB C-36 Plumbing ContractorPlanning and EstimatingHard
A plumbing contractor is preparing to connect a new water heater to an existing residential gas supply line. The existing gas line is 3/4-inch black iron pipe, and the water heater has a gas input rating of 75,000 BTUs per hour. The total length of the gas piping from the meter to the water heater is 30 feet, including an allowance for fittings. Using the provided gas pipe sizing chart (UPC Table 12-8 for 0.5 inches water column pressure drop), what is the maximum BTU/hr capacity for a 3/4-inch pipe over a 30-foot run?
- A85,000 BTU/hr
- B100,000 BTU/hr
- C120,000 BTU/hr
- D150,000 BTU/hr
Show answer & explanationAnswer & explanation
Correct answer: B. 100,000 BTU/hr
According to UPC Table 12-8 (or similar sizing charts for natural gas with 0.5-inch water column pressure drop), a 3/4-inch gas pipe with a total effective length of 30 feet can safely supply a maximum of 100,000 BTU/hr. The 75,000 BTU/hr water heater is within this capacity.
Why the other options are wrong
- A. 85,000 BTU/hr is the capacity for a 3/4-inch pipe over a 40-foot run.
- C. 120,000 BTU/hr is the capacity for a 1-inch pipe over a 30-foot run.
- D. 150,000 BTU/hr is the capacity for a 1-inch pipe over a 40-foot run.
Natural Gas Pipe Sizing (UPC)
The process of determining the correct diameter of natural gas piping to ensure adequate gas supply to appliances, based on BTU/hr demand, pipe length, and allowable pressure drop, as per Uniform Plumbing Code (UPC) tables.
- Uses BTU/hr input ratings of appliances.
- Considers the total effective length of the pipe run (actual length plus fitting allowances).
- Requires consulting specific sizing charts (e.g., UPC Table 12-8 for natural gas at 0.5" WC pressure drop).
- Ensures sufficient gas volume and pressure at the appliance for safe and efficient operation.
Memory trick: BTUs, length, and table chart, play a crucial sizing part.