Journeyman Plumber ExamGas PipingMedium
A plumber is installing a Category I natural draft furnace. What is the minimum required clearance from combustible materials for a single-wall metal vent connector, assuming no special protection is applied to the combustibles?
- A9 inches
- B3 inches
- C1 inch
- D6 inches
Show answer & explanationAnswer & explanation
Correct answer: D. 6 inches
According to NFPA 54 / IFGC, single-wall metal vent connectors serving Category I appliances require a minimum clearance of 6 inches from combustible materials when no special protection is provided. This clearance allows for dissipation of heat to prevent ignition of surrounding materials.
Why the other options are wrong
- A. 9 inches is an excessive clearance for this application and not a standard minimum requirement.
- B. 3 inches is sometimes allowed for certain types of high-efficiency appliance vents or with reduced clearance protection.
- C. 1 inch clearance is typically for Type B double-wall vents or with specific listed protection.
Vent Connector Clearance
The minimum safe distance required between a vent connector and combustible materials to prevent fire hazards.
- Varies by vent type (single-wall, double-wall).
- Varies by appliance category.
- Reduced with approved shielding.
Memory trick: Single-wall, six inches clear, keep the combustibles far from here!