I have a semi sealed grow room that has no ventalation, it gets its fresh air when I visit nightly and open the doors up, and thats it. This was my first grow ever, and I have friends that are experianced growers growing the same strain (Oaksterdam Chemdog #4) and my plants yeilds look nearly the same, yet resin production is awsome and ahead of his, yet he has big can fans pumping. I kept meaning to add ventalation but never got around to it because I didnt want to cut holes in my house.
I dont know if ventalation and O3 are possibly over rated or strain specific, but I can tell you my yeild is looking to be over 1lb with a 1000 watt HPS growing in 5 gallon stand alone DWC. Not bad considering all the misc snags I have had. I can post pics if someonbe wants to see bud grown with no vents running.
I am not advising anyone to grow like this, just saying it worked just fine for me.....