It's not very effective at all to push through a carbon filter.
The only time I'd ever push through one is if I'm pulling through one already and I put a second one on the end for a double filter, but even in that case a inline carbon filter is better imo.
Your losing more air through the ducting than you think before it ever hits the filter, those things are full of pinholes.
Also... when your in a closed system like that I would ALWAYS have the filter in the tent being pulled through, PLUS have secondary filtration for the room. For example a filter with fan mounted on top just scrubbing the room.
In my setup I have a filter exhausting my room, a filter scrubbing my room, a filter in the area outside my room AND a ozone generator for near harvest spikes of smell.
Carbon filters and fan combos are relatively cheap, ~$200 for peace of mind is very cheap. And coming into winter I plan to upgrade my system AGAIN and for every 8 inch fan run a 8 inch splitter to 2x 8 inch duct connected to a 8 inch carbon filter each.
If you cant tell I'm a fanatic.
Edit- I also recommend insulated ducting as it cuts down on leaks a ton
Yes passive is a choice, but not a recommendation.if that's all your situation dictates then by all means just grow! Hell yeah.
But a controlled in and out of circulation is a must for adequate, and more inportantly,even air flow moving.
Remember that his situation is stealth here. You can move more air quietly with bigger fans on low settings with less power.
A speed control on fhe input fan is a must again..at least. Preferably both fans...but why?
I started with passive intake. Carbon filter in the growroom of coarse. Outlet fan pulled through filter and out..
The better your fan. The faster you stitching/seams on your growroom give.
If Tent.not sucking in like a junkie on a crack pipe you need a better fan. Speedcontrol can limit this to a point., but eventually your below cfm to adequately remove smell.
So now we add the intake fan and switch the speed control to this fan....or the tent blows up like a balloon because of the drag filter is causing. This is the worst case scenario. All air is pushed out without filtering.
Best case scenario, speed control on intake and outtake fans.
We can now go as fast or slow as we want during the grow to accommodate the cycle or temps. Slow it down in veg cuz it's not to smelly. Turn them up at flower if you smell anything..
Always have just a little negative pressure in the room. Tent SLIGHTLY PULLED IN.
Notes on second filter. If your room is matched right to your filter and ducting.( 6' at least)...there's info everywhere.... then you won't need one.
I've had police and fire in my house when we had an ailing grandma. They were across the hall from my tent....it wasn't legal then. We had a slotted door to make it worse. I could hear the fan. But no smell.
Buttt if your a freak about it and have the money the second filter is good for when one of the tent ones go out...redundency.also buy a spare fan for this day.
If you do go with a second filter....I wouldn't put it in the area with a filter. I'd use it to catch what the other one missed...outside the room where you don't want smell. You can setup room somewhat wrong with little leaks by accident, but that filter in the tent won't catch the smell that the tent leaked....third filter? lol I digress.
I'm a certified hvac tech. This was my bread and butter. But I'm always learning. Any other ideas?