Hows your grow doing without the CO2 ?I've been wondering this same thing cause I want to get CO2.But I'm going to run my shit just like you(a filtered exaust fan on constantly)
I found a suggestion that said sync your timers to exaust 30 minutes and shuts off,then CO2 comes on for a half hour and shuts off in time for the exaust to come back on this happens all day during the light cycle and at night I think they turned the exaust off .But I don't remember what they did at night with the CO@(Maybe left it on to get to the optimum level for flowering since the dark period is when alot of thc and general flower is produced.)This is what I'm guessing.But smell would still be an issue I think.I guess it depends on how long it takes to stink up the house.