Given: A recirculating industrial direct-fired makeup air heater has a rated input of 200,000 Btu/h...

The applicable provision requires direct-fired industrial air heaters to supply outside ventilation air at a rate of not less than 4 cfm per 1,000 Btu/h of rated input where ventilation air is provided by separate mechanical means. For 200,000 Btu/h , the required outside air is:

200,000 ÷ 1,000 = 200

200 × 4 = 800 cfm

So the correct answer is C