A plumbing contractor is preparing to connect a new water heater to an existing residential natural gas piping system. The contractor needs to ensure the gas line is adequately sized for the new appliance. The water heater has an input rating of 40,000 BTUH. The existing gas meter is 30 feet away from the water heater location. Using the Uniform Plumbing Code (UPC) for natural gas piping, what is the minimum nominal pipe size required if the available pressure is 0.5 psi and the specific gravity of the gas is 0.60?
- A1 inch
- B3/4 inch
- C1 1/4 inch
- D1/2 inch
Show answer & explanationAnswer & explanation
Correct answer: D. 1/2 inch
To determine the minimum pipe size, one must consult the UPC gas piping sizing tables (e.g., Table 12-8, 'Capacity of Pipe of Different Diameters and Lengths in Cubic Feet per Hour of Natural Gas'). For a 30-foot run, 40,000 BTUH (which is 40 CFH for natural gas at 1000 BTU/CF), and 0.5 psi pressure, a 1/2-inch pipe is sufficient. A 1/2-inch pipe can typically deliver over 60 CFH at 30 feet, which exceeds the 40 CFH requirement. (40,000 BTUH / 1000 BTUH/CF = 40 CFH).
Why the other options are wrong
- A. A 1-inch pipe is significantly oversized for this specific appliance.
- B. A 3/4-inch pipe would be oversized for this application, though it would work.
- C. A 1 1/4-inch pipe is greatly oversized and unnecessary for this appliance's BTUH rating and run length.
Natural Gas Pipe Sizing (UPC)
The process of determining the appropriate diameter of natural gas piping based on the total BTUH load of connected appliances, the length of the pipe run, and the available gas pressure, as per Uniform Plumbing Code (UPC) tables.
- Ensures adequate gas supply to appliances.
- Factors include BTUH load, pipe length, pressure, and specific gravity.
- Requires consulting specific UPC sizing tables.
Memory trick: BTUs, Length, Pressure, Specific Gravity – the four pillars of gas pipe sizing.