CSLB C-20 HVAC ContractorHeating SystemsHard
A Category I natural-draft furnace vents into a single-wall metal vent connector routed through an unconditioned attic space near wood framing. Per code, what minimum clearance to combustible materials must this single-wall vent connector maintain?
- A9 inches
- B1 inch
- C3 inches
- D6 inches
Show answer & explanationAnswer & explanation
Correct answer: D. 6 inches
Single-wall metal vent connectors for Category I appliances require a minimum clearance of 6 inches to combustible materials, unless listed and labeled for reduced clearance. This differs from Type B double-wall vent connectors, which typically only require 1 inch clearance due to their insulated construction.
Why the other options are wrong
- A. 9 inches exceeds the standard requirement and is not the typical code minimum.
- B. 1 inch is the clearance requirement for Type B double-wall vent connectors, not single-wall.
- C. 3 inches is insufficient and does not meet code minimums for single-wall connectors.
Vent Connector Clearance
Single-wall metal vent connectors require 6 inches of clearance to combustible materials, while listed Type B double-wall connectors only require 1 inch due to their insulating air space.
- Single-wall: 6 in. clearance minimum
- Type B double-wall: 1 in. clearance (when listed)
- Clearance reduction possible only with listed protective shielding
Memory trick: Single-wall needs six; Type B only needs one.