El Chempo me uses anything but expensive fans. I have a 22" box fan at each end (floor-level) and two oscillating fans at each end, 6' off the ground. One box fan in each greenhouse runs 24/7 and the others are on timers to come on around 9AM and off around 5:00 PM. My 220V heaters are expensive though, at least compared to the fans. Cold damage is my greatest fear.
I would not think there is hear enough carbon monoxide to harm you. I was more concerned about the plants welfare.
