Journeyman Plumber ExamGas PipingMedium
A plumber is installing a gas-fired water heater in a utility closet. The closet has a louvered door, and the appliance requires both upper and lower combustion air openings. What is the minimum required free area for each opening for proper combustion and ventilation, assuming the closet volume is sufficient and the openings are communicating with the interior of the building?
- A1 square inch per 1,000 BTU/hr
- B1 square inch per 2,000 BTU/hr
- C1 square inch per 4,000 BTU/hr
- D1 square inch per 5,000 BTU/hr
Show answer & explanationAnswer & explanation
Correct answer: A. 1 square inch per 1,000 BTU/hr
For appliances located in enclosures communicating with the interior, the minimum required free area for both upper and lower combustion air openings is generally 1 square inch per 1,000 BTU/hr of the total input rating of all appliances in the enclosure. This ensures adequate air supply for combustion and proper ventilation.
Why the other options are wrong
- B. This ratio is typically used for direct outdoor air supply, not interior air.
- C. This ratio is too low and would result in insufficient combustion air.
- D. This ratio is significantly too low for safe and efficient appliance operation.
Combustion Air Sizing (Interior)
Combustion air openings communicating with the interior of a building are sized based on the appliance's BTU/hr input to ensure adequate oxygen for combustion and proper dilution of flue gases.
- Required for proper appliance operation and safety.
- Two openings (upper and lower) are typically needed.
- Size is directly related to appliance BTU/hr input.
Memory trick: BTUs need 'Air' – one square inch for every 'thousand' of 'fire'!