You don't necessarily have to cut holes in drywall to use a carbon filter & can fan. Get the large carbon filter that looks like a small water heater and a good fan that runs a few hundred CFMs. Ideally, you should be able to filter all the air in the room every 10 minutes or so depending on the room dimensions. As an engineer, I'd rather over design the system than buy a bunch of equipment and not have it work. My flowering room is pretty large- 12'Lx24'Wx7'H, and I have zero odor problems. Even when I had 17 large plants in there under two HPS, it didn't smell. Another neat trick is to hook up your A/C air intake so that it's sucking that nice clean air pushed out by your can fan. With getting the oversized can fan and carbon filter, you shouldn't have to cut any holes, since it'll scrub that air in the room several times an hour without having to vent to the outside.