A burner in a gas-fired installation shall be tested and certified by the American Gas Association. A gas-fired boiler shall have a vent or flue that terminates at an acceptable location outside the building. The size of the vent or flue shall be: That recommended by the boiler manufacturer; At least 4 inches in diameter or equivalent area; and If the horizontal run exceeds 10 feet, at least 6 inches in diameter or equivalent area.