Then why have another chemical in the air? I understand your fear of smell.. and as I always recommend, if odor is an issue.. AT ALL then Carbon is the only way to go.. Don't skimp on something that compromises your grow, it's just not worth it, ever. You say you have to have the window open and that's understandable for the cold air intake - but why not get a window fan that covers end to end on the window and sucks air in - then run the carbon filter as well? You'll still lose some efiencey as it's not scrubbing a closed room, but I have an AC in my window with my CF in a closet and it scrubs pretty damn good. Can't smell shit outside, sometimes I'll switch to a window fan and you still can't smell anything outside.. You have the option (because the window is open, it's well ventilated) to run an ozone generator.. but I'm not a big fan of those either, they tend to create health issues.