In the combustion and ventilation air openings size examples, what is the free area of the upper opening?

In the combustion and ventilation air openings size examples, what is the free area of the upper opening?

• A. 250 sq inches
• B. 350 sq inches
• C. 18 sq inches
• D. 36 sq inches

Answer: (D)

Free area is the unobstructed cross‑section that air can flow through. In combustion and ventilation openings, you size this area to meet the appliance’s air needs and the layout shown in the example. For the upper opening in this problem, the given dimensions produce a free area of 36 square inches. If the opening is rectangular, that’s found by multiplying width by height; for instance, a 6-inch by 6-inch opening equals 36 square inches. This size fits the example’s configuration, ensuring enough air can move through without being excessive. The other numbers don’t align with the example’s dimensions or the typical sizing relationships used in these problems—much larger values would imply openings not matching the illustrated setup, and 18 square inches wouldn’t reflect the dimensions provided.

Free area is the unobstructed cross‑section that air can flow through. In combustion and ventilation openings, you size this area to meet the appliance’s air needs and the layout shown in the example.

For the upper opening in this problem, the given dimensions produce a free area of 36 square inches. If the opening is rectangular, that’s found by multiplying width by height; for instance, a 6-inch by 6-inch opening equals 36 square inches. This size fits the example’s configuration, ensuring enough air can move through without being excessive.

The other numbers don’t align with the example’s dimensions or the typical sizing relationships used in these problems—much larger values would imply openings not matching the illustrated setup, and 18 square inches wouldn’t reflect the dimensions provided.