Ok folks, my homelab is in a soundproofed "closet", so it has some fans (2 intake on bottom 3 outtake on top) to dump the heat in the room. They are 33 CFM fans each. At the moment, if I run around 250W (at the wall) of load, the cabinet gets up 25 degrees F (using a raspberry Pi sensor near one of the of fans, it goes from 75 ambient to 100, that's from 24 to 38 C for us in metric lands). The cabinet is 10 cubic feet (0.3 M3).

I want to understand how to make it cooler (A/C is not an option - only fans), but something doesn't add up and I don't understand why: 250W is not a lot, and already 100 CFM of out take and 66 of intake are running full time. I tried multiple ways of calculating this. For example, the CFM = BTU/(1.08 * DeltaF), which says that given 250W, to keep it within 5 F from room temperature, I would need exactly 160 CFM.

Am I using the wrong formula? How do I figure out how much fanning do I need? My final goal is to get to a temperature + watt load -> pwm controlled fan that minimizes noise.