On a side note:

I use a propane log fireplace...as my primary source of heat during the winter.

I let the recirculating fan of the HVAC system run all the time. I assume...my grow room in the rear of the house received some CO2?...I hope so...that shit [propane] cost $600 last winter; while my plants were growing...:thumbsup:

That's as close to a CO2 tank...as they'll ever get...