There are many types of fans that can be used for this job. The two most common types are:
1) Squirrel Cage Blowers
2) Inline Fans
What we want to do is bring fresh air in and exhaust the hot stale air out of the grow area.
Heat rises so at the top of your grow room or cab/closet is the best place for your exhaust fan. Air thats exhausted will be replaced by fresh air provided by your intake.
There are two kinds of intakes
1) Passive Intake
To create a Passive Intake place a hole that you cut in to your cab/closet to let fresh air in. An open window w/ or w/ out a fan would be an example for a grow room.
The exhaust fan located at the top will pull fresh air in through the hole you cut located at the bottom (Recommended for closet grows and cabs)
Example: A fan pulling air out threw the door to grow room would act as your exhaust for a grow room.
2) Active intake
This is the air that is forced in using another blower(recommended for larger grow rooms).
Cold air is heavier then warm air. Cold air is located at the bottom of the cab/closet/grow room.
The best place for your intake is at the bottom of your grow room or cab/closet. I would locate the intake near the floor of your grow room .
Oscillating fans are great for circulating air in the grow room.