Journeyman Plumber ExamGas PipingMedium
A plumber is inspecting the venting system for a Category I natural draft gas furnace. The vent connector from the furnace to the chimney has a horizontal run of 8 feet. The furnace has an outlet collar of 6 inches in diameter. What is the minimum required rise for this horizontal vent connector, according to standard plumbing and mechanical codes?
- A2 inches
- B1 inch
- C0.5 inch
- D4 inches
Show answer & explanationAnswer & explanation
Correct answer: A. 2 inches
Standard codes require a minimum rise of 1/4 inch per foot of horizontal length for vent connectors. For an 8-foot horizontal run, the minimum rise is 8 feet * 0.25 inches/foot = 2 inches.
Why the other options are wrong
- B. Incorrect calculation; this would be for a 4-foot run.
- C. Incorrect calculation; this would be for a 2-foot run.
- D. Incorrect calculation; this is for a 16-foot run or a steeper slope.
Vent Connector Rise
The required upward slope of a horizontal vent connector to ensure proper natural draft and efficient removal of flue gases.
- Minimum 1/4 inch per foot of horizontal run.
- Ensures condensate drainage and proper draft.
- Applies to Category I (natural draft) appliances.
Memory trick: Natural draft needs a RISE to FLY UP and AWAY.