Airflow inside (or outside) the grow room

just in case it was miscommunicated.. the negative pressure bit was about odor only. wherever the carbon filter is drawing air into it, that closed area should have negative pressure to prevent smells escaping via other avenues than the carbon filter... If the carbon filter is sufficient, this will eliminate odor. i actually err on slight positive pressure because i'd rather the walls bow out very slightly rather than bowing inward. I don't have to worry about smell. as far as filters for air quality, yeah the negative or positive pressure really doesn't matter as long as it isn't extreme. If it significantly changes atmospheric pressure, tht will impact VPD calculations too. IT will shift dew point around etc... this is just a guess, but i'd try to stick as close to normal air pressure as possible. if you err one way or the other on purpose for any reason, don't go too extreme. The power / CFM you settle on can be tied to climate control, too.

I’d try to have at least one vent fan pulling hot air out near the top and 2 small fans on either side of the room. If you can have them fit pointed up a bit and oscillating, if oscillating is not an option just try to aim them to blow towards but not too hard on the canopy area from either side.

i would say 2 normal sized ones in each corner. one at the bottom of the canopy and one at the top of the canopy. or just one normal sized one across the canopy with 2 smaller ones laying down flat and pointing upwards, blowing air up through the plants. do more fans with low power or less fans with more power. i prefer to have a few smaller ones to get more coverage across all parts of the tent. but you can get away just fine with just one fan

Circulation fans have been touched on. Exhaust fans haven't really had nuances explained. If you have an AC or a dehuey in your lung room and you are proud of any smells from ruptured trichomes, I pull through the filters such that any bound/unbound water gradients have many linear miles to travel before getting near my flower. If you have low CO2, your best bet is going to be to increase your CFM accordingly. 0101 has a great point with power usage, noise, and mostly work hours....a lot of what we pay for in this industry is a fan at harbor freight or lowes has 1000 work hours on it but a solid grow designed tent might have 3500 work hours. Everything comes down to time at the end of the day, even your fancy LED boards will go to shyte. This is why you see huge 300 piece lots of 4x4 light fixtures for fifty or a hundred bucks each....because they're basically scrap now but people don't understand that and buy them up. I disagree with 0101 about always negaative pressure when using a filter, what if you are filteringh for your tent, not from?

You want gas exchange and circulation Enough gas exchange has to occur to maintain levels of o2/co2 etc in the grow area. Otherwise during the lights-on cycle the o2 will spike and co2 will diminish and co2 is your limiting factor. "They" say 3-5x CFM of volume of tent -- ~150CFM, give or take. This seems excessive but at least it is a safe target even if a bit overkill. A tent in a small room may not be enough. whether air flows from the rest of the house or you exhaust outside, you need something exchanging fresh air. I have a 10x10 that is only half-filled or less with plants, so effectively more like a 5x10. I run a couple 6" intakes at 30-40% and a 8" exhaust at 30-40% - adjusted to prevent bowing of walls in either direction. This is definitely less than 3x suggestion above and i have had no negative impacts to production compared to over-doing it the past. Go bigger with equipment because running at lower power is quieter and the equipment probably lasts longer, but don't flip out too much if your CFM falls a bit short of what 'they' say. * - you want slight negative pressure in tent if making use of a carbon filter. otherwise i go with no bowing of walls or allowing a slight bowing outward vs inward, since you don't lose volume in the tent that way. Better to stick as close to normal atmospheric pressure, i'd assume, so avoid extremes in that regard. Circulation just has to cause some gentle jostling throughout your plant's canopy. That tells you plenty of air is moving around. Too much and you cause wind burn - whether to leaves or pistils. As far as gas echange is concerned, buy a duct fan that's larger than you need and run at 30-50% power. This will be the quietest option and well worth the extra cost. With circulation you can go small or big. a bigger fan pointed over the top will almost certainly cause a ton of air movement all throughout a small enclosed area. or a couple well-placed small / gentle fans can work too. Have them pushing air to create a vortex as best you can - work together not competing. This is something i've slimmed down over time, too. I used to have 2 box fans hanging and 2-3 oscillating clip fans distributed. Overkill is an e-peen. Now, it's just the 2 box fans set on low far enough away that it jostles canopy and bounces off far ceiling/wall and rolls underneath canopy "enough." If you have consistent growth throughout canopy and avoid mold and such long-term without exception, it is sufficient. Not overcrowding your canopy is also integral. That's just shooting yourself in the foot before you start.

2 little ones or one oscillating

I would at least use 2. Depends on your growing style, one above Cannopy, one under cannopy… I am a Fan of great air circulation, i currently use 4 fans in an 120x60x160

Hey Growmie! Put at least one oscillating fan above the canopy and once you reach bloom I would place a second one beneath the canopy. Consider lollipopping for to allow airflow! To start the obvious, a duct fan also improves air movement! Enjoy and keep growing!