Carbon Filter

Hi guys just finished making my own grow box thanx to all your help on these threads. I'm just about to install my diy carbon filter and had a question. Does it have to be on the inside of the box or can it be on the outside? I have an exhaust fan on top of my box and I'm trying to save room in my box so my light can go higher. Do carbon filters work if they push the air threw them? Or do they only work if they suck the air threw them? Thanx in advance for any help, happy growing.

They work either way but i find it better if you suck the air through the filter other than push it out.