I have a 120mm that I want to put into my case but I can't decide whether it would be more beneficial to put it on the side panel where there are currently no fans or on top with another fan. If I put it on the side panel should I put it as an intake or exhaust fan? Thanks for your input.
imo, for intake put it as low as possible (heat rises) and obviously visaversa. i run 4 120mm (2 attached to a h100i) + 200mm intake and only 120mm exhaust and my cpu temps never hit 30oC, gpu never hits 450C and my sshd never hits 30oC. this is all at load
Assuming you have a tower case. If you have a flat cpu cooler that pushes air at the cpu, then it could make sense to have an intake fan on the side, to supply the cpu fan with fresh air.
Otherwise, I think it makes more sense to put your fan on top, especially if the PSU is on the bottom. Depending on other details the hot air can exit the case by itself but it's effective to have a fan up there to help it on its way.
I don't really suggest using a side fan at all, it will interfere with the mounting of any decent CPU cooler due to height restrictions. I am guessing you have a front intake fan and a back and top exhaust fans, right? The airflow in your case will be from the lower front of the case to upper back and top, putting a fan on the side will interfere with that airflow no matter the configuration (intake or exhaust).
If you want good cooling, the amount of air being pushed into your case by the intake fans should be equal to the amount of air sucked out of the case by the exhaust fans. Try to put the extra in such a way that you have the same number of intake fans as exhaust fans.
If you are already have the same number of intake and exhaust fans, then put it at the top.
And about heat rising. I sincerely doubt that the amount of air displaced by the current created by the difference in pressure (due to different temperatures) inside the case will ever, ever be equal to the cubic feet of air per minute that one normal fan displaces.
i think it depends on the config / parts in your machine. Personally i have Vengance C70 with an H100i in the top of the case and i use top most side fan space for a 120mm fan to cool the vcore but if you have a tower heatsink i'm not sure you'd get any benefit.