If not legal,... hell i am, and i still think you gotta get a Can33 or something with a minimum flow rating on it, so you know to even under flow that. At least thats how i do it. It works out to $8 a month for guaranteed odor control, you can't beat it. Oh also if this is in a room with a home HVAC vent, make sure to seal it off, or when it blows air into the grow room it will most likely overpower your exhaust fan, and during that time, no more negative vacuum, and smell being pushed out every crack. I sealed mine off at first, but then decided to reroute it, to also blow into my attic,.. after going THROUGH the back half of the 7000BTU AC unit i have in the room, the back half is where the compressor and hot components are, so now the fucker runs efficient as hell. I cool my 12x12 grow room with high ceilings for $30mo in the heat of the south west deserts