A space with a sloped ceiling that increases in height from the operable opening is to be naturally ventilated. The ceiling height at the opening is 8 feet and increases to 16 feet at a point 20 feet away. What ceiling height (H) should be used to calculate the ventilated floor area distance for a single-side opening?

• The calculation cannot be performed; mechanical ventilation is required.
• 8 feet (the minimum height)
• 12 feet (the average height within 20 ft)
• 16 feet (the maximum height within the space)