Journeyman Plumbers Exam Gas Piping and Appliances 4 — Questions and Answers
Question 1: Under NFPA 54, what is the required location for the manual gas shutoff valve for a gas appliance?
- At the meter only
- Within 6 feet of the appliance in the same room (Correct answer)
- On the appliance itself
- In an adjacent utility room
Correct answer: Within 6 feet of the appliance in the same room
NFPA 54 requires an accessible shutoff valve within 6 feet of each appliance and in the same room so it can be reached quickly in an emergency.
Question 2: A gas water heater installed in a garage must have its ignition source elevated at least:
- 6 inches above the floor
- 12 inches above the floor
- 18 inches above the floor (Correct answer)
- 24 inches above the floor
Correct answer: 18 inches above the floor
To prevent ignition of heavier-than-air flammable vapors that settle near the floor, ignition sources in garages must be 18 inches above floor level.
Question 3: Which of the following is the correct way to check for a gas leak at a connection?
- Use an open flame to detect combustible gas
- Apply listed leak detection solution and observe for bubbles (Correct answer)
- Listen carefully for a hissing sound only
- Use your sense of smell exclusively
Correct answer: Apply listed leak detection solution and observe for bubbles
Listed leak detection solution (or an electronic gas detector) is the approved method; open flames are dangerous and smell alone may miss small leaks.
Question 4: What is the minimum pipe size for a gas supply line serving a residential furnace rated at 100,000 BTU/hr at 100 feet from the meter with ½ inch WC pressure drop?
- ½ inch
- ¾ inch (Correct answer)
- 1 inch
- 1¼ inch
Correct answer: ¾ inch
Using NFPA 54 sizing tables for natural gas at low pressure (0.5 in WC drop), a 100-ft run at 100,000 BTU/hr typically requires ¾-inch pipe.
Question 5: A Type B gas vent used for a Category I appliance must maintain a minimum clearance to combustible construction of:
- 0 inches (it is rated for zero clearance)
- 1 inch (Correct answer)
- 2 inches
- 6 inches
Correct answer: 1 inch
Listed Type B double-wall vents are designed for 1-inch clearance to combustibles, which is their primary advantage over single-wall connectors.
Question 6: When two or more gas appliances are connected to a common vent, the common vent must be sized based on:
- The largest single appliance connected to it
- The combined BTU input of all appliances connected to that common section (Correct answer)
- The smallest appliance to avoid backdrafting
- The average BTU input of all connected appliances
Correct answer: The combined BTU input of all appliances connected to that common section
The common vent section must handle the combined input from all appliances that can operate simultaneously, so total BTU capacity is used for sizing.
Question 7: An appliance connector made from aluminum is prohibited for use with:
- Natural gas only
- LP (propane) gas only (Correct answer)
- Both natural gas and LP gas in mobile homes
- All gas appliance connections regardless of location
Correct answer: LP (propane) gas only
LP gas (propane) contains chemical additives that react with aluminum, causing corrosion and eventual failure; aluminum connectors are prohibited for propane service.
