How much outlet fan needed??

So I’m a newbie to the indoor grow. And it’s been many years since I was active in the outdoor scene. I’m trying to get all my variables dialed in.
My space is a 2x6’ closet w/ 8’ ceiling. I’ve got a new HLG 320xl full spec LED, which is plenty for that space.
My question is about my airflow in and out. Before my first grow I installed a 6” Hurricane exhaust fan vented to the attic through the closet ceiling. My only inflow is passively under the door. There’s about a 1.5” gap that’s between the door and concrete floor.
This first grow has been fun and I’ve learned a ton. I have no trouble keeping the space as cool or warm as needed. But with the exhaust running it literally sucks all the RH up and out. I’ve bought a speed control for the exhaust fan and it helps some, but even on low I have to keep 2-3 humidifiers running full blast to get my RH to necessary levels.
If I turn the exhaust off I can dial in any combo (of temp and RH) easily and it stays constant. I wanna know do I need the exhaust fan to run all the time?? Some of the time? Not at all?
My understanding is that the plant needs a constant new supply of air…..without the exhaust pulling in (from under the door) and venting out (into the attic) could the plants thrive?
If it’s a matter of CO2, I would rather buy and run a tank of CO2 than deal with the exhaust and 3 humidifiers that need filling daily.
I know I can buy a control that would only turn the exhaust fan on if the RH got too high….but I can regulate that variable and be stable at whatever level it needs to be and don’t need the exhaust for that purpose.
Can someone tell me what the deal is ? My life would be much easier if I could just dial in my VLD and let ‘em grow. Thanks all.

Venting directly into the attic is bad news

All that RH you’re losing with the exhaust is all going into the attic insulation slowly but surly

Ambient co2 is just fine for your space imo.

bk78 said:

Venting directly into the attic is bad news

All that RH you’re losing with the exhaust is all going into the attic insulation slowly but surly

Ambient co2 is just fine for your space imo.

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Ok lemme see if I can interpret your input. The worry with the rh going into the attic is that it’s bad to have too much moisture in the attic? I should have clarified. The closet is in a small one room guest cottage, that I use for my home office. The attic is a very small maybe 2’ tall space that is basically outside. Nothing is stored there…..it’s only there because the pitch of the roof created the extra space. On either side of it are vented grills to the outside that keep the birds out. So for all intent and purposes the exhaust is going directly outside.
As for ambient CO2, what does that mean? That the CO2 that’s already being produced will be fine for the space? I’m in the office a lot, everyday…..and of course I’m always opening the door peeking at the plants. Not sure how much of anything that generates but there is activity around the space and in the room.
Would you conclude that I could do away with the exhaust and, as long as I keep my RH and Temps in check, I wouldn’t notice a difference??

Bullmark said:

Ok lemme see if I can interpret your input. The worry with the rh going into the attic is that it’s bad to have too much moisture in the attic? I should have clarified. The closet is in a small one room guest cottage, that I use for my home office. The attic is a very small maybe 2’ tall space that is basically outside. Nothing is stored there…..it’s only there because the pitch of the roof created the extra space. On either side of it are vented grills to the outside that keep the birds out. So for all intent and purposes the exhaust is going directly outside.
As for ambient CO2, what does that mean? That the CO2 that’s already being produced will be fine for the space? I’m in the office a lot, everyday…..and of course I’m always opening the door peeking at the plants. Not sure how much of anything that generates but there is activity around the space and in the room.
Would you conclude that I could do away with the exhaust and, as long as I keep my RH and Temps in check, I wouldn’t notice a difference??

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Ambient co2 means the ppm level of it in your office, which I’m 90% sure is higher than others with you being in the office a lot

Im sure your RH levels are fine as well

Exhausting will be needed for the smells of course, but it’s not needed if you don’t care about smells.

bk78 said:

Ambient co2 means the ppm level of it in your office, which I’m 90% sure is higher than others with you being in the office a lot

Im sure your RH levels are fine as well

Exhausting will be needed for the smells of course, but it’s not needed if you don’t care about smells.

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Excellent. I’m just about to chop my grow and start another soon after. I’ll give it a go sans the fan and see how she does. Thanks for the input.

Bullmark said:

Excellent. I’m just about to chop my grow and start another soon after. I’ll give it a go sans the fan and see how she does. Thanks for the input.

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Happy harvest

Bk is correct, you do not wanna exhaust into an attic.

Look at sealed grows or exhaust properly out