vertical space saved my 2x2 smell situation

The filter sizing point is real and I don't see it talked about enough. But I'd push back slightly on the "replace carbon before flower" as a blanket rule. I've gotten 18 months out of a Phresh filter running two cycles a year growing some genuinely loud terp-heavy stuff, because I keep humidity in check and never let the carbon get wet. Moisture is what actually kills carbon, not time alone.

What wrecked my old filters faster than anything was sweating plants late flower with humidity spiking. If you're running a proper VPD curve through the whole cycle and your room stays dialed, that carbon lasts way longer than a year.

The ceiling-mounted fan and filter setup though, fully agree. Night and day for actually containing smell in a small space. I run mine that way in a 3x3 and the negative pressure is just cleaner when everything is up high.

the two smaller plants thing resonates hard with me, i run a perpetual setup and keeping individual plants compact just makes everything easier to manage, not just smell.

one thing i'd add that nobody mentioned yet is airflow direction inside the tent mattering almost as much as filter placement. if your fan is pulling air from the top but your plants are creating dead pockets lower down, you can still get smell buildup near the floor and around the base of the pots. a small clip fan circulating air from the bottom up ties the whole system together. the filter does the scrubbing, but you need the air actually moving toward it first.

on the filter lifespan debate, both points in this thread are fair. humidity is the killer, yeah, but so is just running hot and heavy through multiple cycles without a break. i've had filters that looked fine and tested borderline in year two. at that point it's kind of a gamble during a heavy flowering strain and i'd rather just swap it.