I can't seem to send you a pm in response to your question. Anyway, I'm computer controlled in regrads to co2, and run a sealed room environment. That said, it would be impossible for you to do what I do. All you need is fresh air to come into your space at a regular interval. If you can get a recycle timer and put an inline fan on it, even a cheap one thats a booster fan, just set it to run every hour or so, for a few minutes. If you pull in fresh air from another room, or outside, depending on the temp, then you'll have all the co2 you really need. Getting levels like 1200-1500 ppm are only necessary if you're trying to dial in a hightech grow.
Good luck...let me know if I can help with anything, anytime.
Good luck...let me know if I can help with anything, anytime.