Just throwing in my two cents, I have a closet grow going on with a 400w HID bulb which obviously puts off lots of heat. I have an inline fan with a carbon filter, which together completely 100% remove all smell. The venting situation is set up thusly: I draw air out of the closet from the top of it, and blow it out the top as well, while passively drawing fresh air through a hole in the bottom. This alone is enough ventilation during fall/autumn, and during the summer I just set up a regular window fan drawing air in to the room with the closet to keep it as close to ambient temperature as possible without many issues. Sure, when it's 98 degrees out I will turn the light down to about 50% just because it's too damn hot in general, but otherwise it works like a charm. Basically what I'm trying to say is that if temps are your main concern, you can almost certainly just vent directly into the room through a carbon filter as long as you're not in some tropical region where it's hot all year round.