Will this Ona gel work for a closet grow with three plants in the back of my house? Or will i need to come up with some way to seal my closet and have an outake fan with carbon filters attached?
Measure your closet and figure out the volume in cubic feet. Ideally you want to be able to turn over that volume of air at least once per minute (more is better in this case). Buy the fan with the proper cfm and vent it to the outside and you will have enough net negative air pressure in the room so that odor should not be a problem. If you are worried about noise from fan vibration, be sure to use some rubber between the fan mounting brackets and the wall.
In my mind, a carbon filter is the only answer to this question. Any other alternatives, even ONA only cover up the smell, a carbon filter is the only thing that actually removes the smell from the air besides maybe ozone.