I’m using an AC infinity 6” fan in a 4 x 4 tent which is a fairly high end fan with probe and controller etc and definitely an overclock for a 4 x 4 as I originally got it as a top end fan for a 5 x 5, I get the importance of an exhaust fan to control odor mainly but secondary as a means to control temperature but honestly in my limited experience I’ve found exhaust fans to be almost completely ineffective as a means of controlling temperature, especially when compared to what a cheap 4” inlet fan can do in comparison with just general room temperature air, let alone air conditioned air, why do I see exhaust as the primary source for temperature control everywhere, am I missing something?
I don't know your experience with growing tents but for an exhaust fan to be effective in controlling temperature, several precautions should be adhered to, and you might know all of these but I'm just saying:
1- intake vent should be at a low point in the tent in order for the air column to span the whole tent.
2- intake vent size should ideally be 1.25 to 1.5 times the size of your exhaust fan inlet to insure you're maximizing the utilization of your exhaust fan.
3- In case you have an air filter on your intake, then the intake size should be enlarged to at least 2 times the size of your exhaust fan inlet and to further increase the intake size according to the air filter's resistance.
4- To make sure that there are no points above the plants that can act as an air intake because this will simply create an air stream inside the tent that have a reduced effect on hot air around the plants.
I think, and this is only my theory, the prevalence of exhaust fans compared to inlet fans is that this idea is borrowed from greenhouses. Greenhouses typically use exhaust fans and create negative pressure inside them and I think people just followed suit. Some green houses of course use inlet fans to create positive pressure inside and this has the added benefit of preventing dust and insects from entering. On the other hand, a lot of marijuana growers might want to control the odor at some point in the future, so installing a fan in an exhaust configuration would allow them to easily install a carbon filter afterwards but a lot of people just follow what's popular without giving it much thought.
Exhaust fans are also typically used in computer cooling. Over-clockers and people using powerful GPUs add one or more inlet fans along with the exhaust fan(s). Manipulating the power of the exhaust and inlet fans would allow them to create either negative pressure, positive pressure or a balanced one.
From what I know, installing a fan in the inlet configuration should be slightly (just slightly) more efficient than installing it in an exhaust configuration. The inlet configuration can also create better temperature gradient inside the cooled space. For best cooling effect, both an inlet fan and an exhaust fan should be used and using only one is just an acceptable compromise.
The exhaust pumps the air out the window but the inlet just pulls from my living room which is generally reasonably cool, around 70. I guess the cooler air going in is far more important than the hot air being pulled out, hence my fascination with exhausts being the main tool for temperature control in most grow room information sources.
My exhaust fan is far more powerful, I bet if I reversed the fan positions it would be far more effective.
Inlet fans create a noticeable breeze directly on or around the plant which helps them decrease their temperature more than what would happen if an exhaust fan is used.
