Plumbing Gas Piping Systems 2 — Questions and Answers
Question 1: When sizing a natural gas pipe, which of the following factors is NOT used in the calculation?
- Total length of the pipe run
- Total BTU demand of the appliances
- Color of the pipe material (Correct answer)
- Allowable pressure drop
Correct answer: Color of the pipe material
Gas pipe sizing is based on BTU demand, pipe length, and allowable pressure drop — pipe color has no engineering significance in sizing calculations.
Question 2: What unit is commonly used to measure low natural gas operating pressure in residential systems?
- Pounds per square inch gauge (PSIG)
- Inches of water column (in. WC) (Correct answer)
- Millibars (mbar)
- Pascals (Pa)
Correct answer: Inches of water column (in. WC)
Inches of water column (in. WC) is the standard unit for low residential gas pressures, where 27.7 in. WC equals 1 psi.
Question 3: Which type of fitting is NOT permitted for concealed gas piping inside a building?
- Welded joint
- Threaded joint with approved pipe sealant
- Brazed fitting (where approved)
- Compression fitting (Correct answer)
Correct answer: Compression fitting
Compression fittings are not approved for concealed gas piping because they are mechanical connections that can loosen over time and are not reliably gas-tight.
Question 4: What material is PROHIBITED for use as interior gas piping inside a residential building?
- Schedule 40 black steel pipe
- Corrugated stainless steel tubing (CSST)
- PVC or CPVC plastic pipe (Correct answer)
- Copper tubing (where permitted by local code)
Correct answer: PVC or CPVC plastic pipe
PVC and CPVC plastic pipes are not approved for interior gas service because they cannot withstand gas permeation, heat, and physical damage requirements.
Question 5: Where must a manual gas shutoff valve be installed for a new gas appliance?
- At the gas meter only
- Within 6 feet of the appliance in the same room, in an accessible location (Correct answer)
- In the main electrical panel room
- Outside the building near the foundation
Correct answer: Within 6 feet of the appliance in the same room, in an accessible location
Code requires an accessible manual shutoff valve within 6 feet of each gas appliance in the same room so it can be quickly reached in an emergency.
Question 6: What is the maximum typical low-pressure natural gas system operating pressure for residential appliances?
- 0.5 psi (14 in. WC) (Correct answer)
- 2 psi
- 5 psi
- 10 psi
Correct answer: 0.5 psi (14 in. WC)
Residential natural gas appliances typically operate at low pressure — commonly 7 in. WC for most appliances, with a maximum of about 14 in. WC (0.5 psi) at the appliance.
Question 7: What is the minimum required separation between a gas meter and electrical service equipment?
- No minimum separation required
- 3 feet (Correct answer)
- 5 feet
- 10 feet
Correct answer: 3 feet
Most codes require at least 3 feet of clearance between a gas meter and electrical service equipment to reduce the risk of a spark igniting a gas leak.
Plumbing Gas Piping Systems 2
When sizing a natural gas pipe, which of the following factors is NOT used in the calculation?