It's been about 3 years since I installed the one on my 3.6. IIRC it actually pulls air from the bottom of the housing which I think is ducted into the radiator support so it actually pulls air from outside the engine compartment. The rubber seal around the top is to seal it to the hood to keep the hot air out.

That said I bought it more for the look and sound rather than expecting a big h/p increase. The factory isn't leaving any easy h/p laying around much these days.
Dallas