thanks for the help guys! so if i got a carbon filter i should expect my temps to increase due to less air flow and less heat being removed?
Just oversize it. If your tent is 4x4x7 tall, that's 112 cu. ft. Get a filter that's spec'd for something significantly larger. Like 220 cu. ft. (while keeping an eye on whether it will fit inside your tent. (You can also put the fan outside the tent to reduce space used?). Also use a larger fan. You can always use a rheostat device to dial down the speed to meet your temperature requirements.
You can also use a device like this
Quantum Variable Speed Controller. With this device you can set the normal fan speed for necessary air replacement (so the air inside tent is replaced every 5 minutes. I.e., 25 cfm. But, this device will kick the fan up to full speed if the heat rises past your pre-set threshold.).
Side note: I like to use a variac ($50 US) which reduces the voltage (instead of clipping the sine wave, like these less expensive controllers). The fan runs quieter. I've read fans last longer with clean voltage like this too.
If you or someone you know is good with electronics, it should be possible to wire a variac to a thermostatic switch in a way that when the switch is off (below the preset temperature), the variac sends something like 50 volts to the fan (slow speed). When the switch is on, it sends full 110 volt (high speed) to the fan, bypassing the variac. It should just be a matter of diodes to block the direction of electricity. Maybe a relay.
Someday I'd like to work this out because I really prefer using a variac instead of a simple wave-clipping device which I'm pretty sure the Quantum is. The wave clippers are like switching the fan off/on 60 times a minute (for micro- to milliseconds depending on how slow the fan is desired to run).
