A space with a sloped ceiling is to be naturally ventilated from a single side opening. The ceiling height at the wall with the opening is 8 feet and increases uniformly to 16 feet at a point 24 feet into the room. What is the ceiling height (H) used to calculate the maximum ventilated depth?

• 8 feet (the minimum height).
• 16 feet (the maximum height within the space).
• The average height within the first 20 feet from the opening. The calculation requires knowing the height at 20 feet.
• 12 feet (the average of 8 and 16).