Temp too high...switch fan around?

I have a pc fan in the bottom of my grow box exhausting air out, and an intake hole at the top above the lights. The temps are in the mid to upper 80's inside the box. Do you guys think it would be a better idea to switch the fan around so that it is intaking at the bottom and exhausting at the top above the lights?

I have four CFL's also. No lights that really produce a lot of heat.

well, CFLs still produce heat, and if you have them next to your intake hole then you are heating the air (albeit not by much) that you are sucking in. It would be a good idea to have intake coming from somewhere cool rather than somewhere warm, if your grow area is getting too hot.

I might also suggest another PC fan at the top to increase your airflow, because unless you have a huge PC fan, then you really don't have that much airflow. Of course the fans should be pushing air in the same direction, thus the bottom as intake and the top as exhaust.

Additionally, plants consume CO2 through the bottoms of their leaves and vent moisture through the tops. Having your airflow come from the bottom actually seems pretty logical to me. That would, in theory, push fresh air past the bottoms rather than the tops so that there is more airflow where you want it most.

If you follow all these you should see a 5-10 deg (F) drop.

Out of curiosity, do you have the PC fans hooked up to a PC to control the temp? I'm currently looking into a method of setting up a computer to control the air temp via pc temp sensors and pc fans. (I should make another thread about that probably.)

It's well know that heat rises....so if your intake is on the low side it forces the hot air to the top of your cab....it would make sense to have your out take at the top of your cab being as thats where your hot air is....Logical

Hey guys thanks. Yeah I never worried about the temps until recently because every time I would open up the box it would be real warm air that came out. I have a clock with an outside wireless thermometer so I put the thermometer in the box today. Temps went up to 86-87. Then I just peeled away the silicone sealing the fan, pulled it out and flipped it around. Temps went down to 74-75 in about an hour.

The only thing I'm worrying about now is that while the lights are out they will be too cold. Right now it is 63 in there, but its also 63 in my room so that might make sense. (windows open)

One more question...should the fan stay on all the time or only while the lights are on? My guess would be all the time because the plants never stop growing and still need fresh air even without lights. They actually store the energy from the light and use some of it when the lights are out. Is my guess right?

metagrower - I bought the fan from radioshack and cut the pc power supply wiring off. Then I spliced the wires and hooked them up to a 12V AC/DC adapter (power adapter). So no, its not hooked up to a computer to control it, but that sounds like it could be a good idea if you could make/get a program to control the fans.

Well, actually from what I understand plants don't grow at night. With no light to perform photosynthesis with they basically "sleep". At least, that's my understanding. Thus you wouldn't need to keep your fans on at night. It is, however, good to have a drop in temp at night (up to 10 deg F) simply because it is more natural. I like to think of my plants as little living creatures I'm playing God with, and so I like to keep them in good spirits. I imagine that they probably stress a bit with all that induced growing and need the sleep/break, just like we do. But I am pretty certain that you are correct, if you over-feed them light, they store it up and use it when the lights go out. Either way, it's not going to hurt them. I'd be curious to find out the results of experimentation.

As for the computer controlled setup, I'm finding that this is not far off from X10 home automation, which is really pissing me off, cause that crap is not cheap. I think I'm going to wind up building my own PC card and writing the driver code myself. Yeah right. I'm a stoner. We'll see if I ever get around to it. But damn it sounds like a good idea.