Thanks for the advice... I always thought your were supposed to pull air through your carbon filter as apposed to pushing air through it?
The issue I have with pulling air through the carbon filter is that you add a number of other variables that effect the efficiency of the filter. Humidity being the big one.
Im honestly not to worried about the smell of the upper cab, im going to be growing autoflowers with low ambient smell during flower.. Mostly Purple Jems..
Cool
So What if i ran the ducting so it exhaust's the lower cab with 400w cooltube, then ducting from the 250w cooltube to the fan, then vent hot air out of the room, then i can just get a separate smaller fan to exhaust the upper cab..
That will work
(guess im still kinda confused where the carbon filter should go, i had it on the end of my cooltube last grow and had absolutely no smell leakage.
If it works for you keep doing it.
Fan and Carbon Filter Placement
If no carbon filter is being used then place the fan at the highest possible point in the room; the reason for this that hot air rises and it is the hot air that needs to be exhausted. Also, place the fan on the opposite side of your intake. The negative pressure that the fan creates in the room will pull air from the intake opening across the garden and towards the fan. This will bring the fresh air over the plants while displacing the old stale air.
If a carbon filter is being used then place the fan on top of the filter. There are two options that a grower can use with the carbon filter: 1) Suck through the filter or 2) Blow through the filter.
Sucking air through filter is the preferred method. Carbon filters should be placed on the floor standing upright or hung horizontally from the ceiling. Place the fan and filter in the room opposite the intake port. From the fan, attach ducting so as to exhaust the scrubbed air out the room. Keep the ducting as short as possible and avoid any bends in the ducting. Keeping the ducting as short and as straight as possible will reduce the friction loss and noise.
Blowing through the filter is a less commonly used method of exhausting. The benefit is that the fan can be placed at the highest point in the room and the hot air is sucked out of the room and forced through the filter. However, if you're using the fan/filter combination as part of your exhaust system (as opposed to just an odor scrubber), it will need to be placed outside of the growing area.
Before using a carbon filter for the first time always take the filter outside and then first suck, then blow through it before installing it in your growing area. This will blow out any carbon dust which is created in the filter during transport. During normal operation always keep the dust sock on the filter; this stops large dust particles from blocking the filter and will help prolong the life of the filter.
Came from here
http://www.bghydro.com/BGH/static/articles/0606_vent.asp
