A naturally ventilated space has a sloped ceiling that increases in height from 8 feet at the operable wall opening to 16 feet at a point 25 feet away. For the purpose of calculating the maximum ventilated floor area distance, what ceiling height (H) should be used?

• The maximum ceiling height of 16 feet.
• The ceiling height at the midpoint of the room, 12 feet.
• The average ceiling height within 20 feet of the opening.
• The minimum ceiling height of 8 feet.