ppm of Co2 in our air we breathe is about 400 ppm. In prehistoric days it was closer to 1600 ppm. 1500 ppm per sq. ft. would probably kill you & everything in your house. I have a 5' x 10' tent which is 50 sq. ft. That would be 75,000 ppm of Co2. No chance I'll ever try that. That's why you use something like an Atlas Co2 Controller with a sensor. Once you set it (Usually 1200 - 1500 ppm) if the Co2 gets over that the sensor shuts it off. The best temps for Co2 are 84 F - 94 F. I found an excellent article on it that tells you all you need to know. It's on a site called Grow Weed Easy or ILGM; can't remember which one.isn't 1500 ppm per ft needed (co2) ?