Journeyman Plumbers Exam Gas Piping and Appliances 2 — Questions and Answers
Question 1: What is the minimum clearance required between an unprotected gas appliance vent connector and combustible material?
- 6 inches (Correct answer)
- 9 inches
- 12 inches
- 18 inches
Correct answer: 6 inches
NFPA 54 requires a minimum 6-inch clearance between an unprotected single-wall metal vent connector and combustible materials.
Question 2: Which pipe material is NOT approved for use with natural gas in residential installations under NFPA 54?
- Black steel pipe
- CSST (corrugated stainless steel tubing)
- Copper tubing (Type K or L)
- PVC plastic pipe (Correct answer)
Correct answer: PVC plastic pipe
PVC plastic pipe is not permitted for gas piping because it cannot withstand the temperatures and pressures involved and is not listed for gas service.
Question 3: A gas appliance draft hood is designed primarily to:
- Increase combustion efficiency
- Prevent backdrafting from affecting burner operation (Correct answer)
- Reduce gas consumption
- Filter combustion air
Correct answer: Prevent backdrafting from affecting burner operation
A draft hood (or draft diverter) protects the appliance burner from downdrafts and pressure fluctuations in the venting system.
Question 4: When sizing a gas piping system, the pressure drop allowed in a low-pressure system (under 2 psi) from the meter to the appliance is typically:
- 0.1 inch WC
- 0.5 inch WC (Correct answer)
- 1.0 inch WC
- 2.0 inch WC
Correct answer: 0.5 inch WC
For low-pressure systems, NFPA 54 sizing tables are based on a 0.5 inch WC pressure drop from the meter to the most remote appliance.
Question 5: A gas dryer vent must terminate:
- Into the attic to keep moisture away from living areas
- At least 3 feet from any opening into the building (Correct answer)
- Into the crawlspace
- Through the floor to grade level
Correct answer: At least 3 feet from any opening into the building
Dryer exhaust vents must terminate outdoors at least 3 feet from any building opening such as windows, doors, or vents to prevent re-entry of combustion products.
Question 6: What type of fitting is prohibited in a concealed gas piping installation?
- Welded fittings
- Mechanically formed tee fittings listed for gas
- Compression fittings (Correct answer)
- Threaded fittings
Correct answer: Compression fittings
Compression fittings are not listed for gas service and are prohibited in concealed gas piping installations where leaks cannot be easily detected.
Question 7: The purpose of a sediment trap (drip leg) installed at a gas appliance is to:
- Increase gas pressure to the appliance
- Catch moisture and debris before they reach the appliance valve (Correct answer)
- Regulate gas flow rate
- Serve as a shutoff point during emergencies
Correct answer: Catch moisture and debris before they reach the appliance valve
A sediment trap collects condensate and pipe scale that would otherwise clog or damage the appliance's gas valve and controls.
