Ventilation setups are actually differentiated by how the fan and the filter are placed. Broadly speaking, there are actually four different kinds of ventilation setups for grow tents:
Fan in, filter out
Filter in, fan out
Fan in, filter in
Fan out, filter out
Most growers prefer the third method here where both fan and filter are inside the grow tent because that offers an excellent control over the air flow as well as the smell. However, different methods have different benefits and drawbacks and this is something that growers prefer on a case-to-case basis.