Intake or exhaust

Yes, you will want to have an exhaust fan for your case, so install it as one  

If you have no intake at all, it will be wiser to use the fan as an intake instead of an exhasut to keep the air pressure in the case high. tecmo, am I lying...?

Higher air pressure means more air particles means better cooling?

What case do you have and how many case fans does it have?

You should always have negative air pressure, i.e more air being sucked out than sucked in. So not having an intake fine shouldn't be an issue, as air will find a way in through any holes in the casing.

There is a fan on the heatsink and a fan with the power supply. I posted the cpu and core temps in a thread over a year ago, I checked them again and they're just about the same as they were then.

i'm going to get the cpu and heatsink cleaned and then install the case fan and see how things are