Grow Box Temp Increase with Circulation Fan on?

Whats up RIU, i've learned a lot from you guys, I'm hoping you'll be able to shed some insight to my current issue.

I've got a stealth box made of MDF with dimensions of 30"x18"x48"

Two exhaust fans are on the side walls (18" long side) at the very top, on opposite sides.
I have a 8" fan secured at the top of the box blowing down over all the CFL's, and the top of the plants.

I accidentally left the 8" fan off last night and noticed something funny.

With the 8" fan ON, the temp was 86.1 F
With the 8" fan OFF, the temp dropped to a reasonable 81.1 F

I tried this a few times throughout the night, making sure the room's ambient temp remained the same. Every time there was a difference of 5-6 degrees F

Does anyone have any suggestions as to why this would be happening? I understand I need the circulating fan to strengthen the stalks, but should I be putting it in a different position?

Currently it is secured at the top of the box blowing straight down. Probably about 4" to the left is one 80mm exhaust fan, and 4" to the right is the other 80mm exhaust fan.
Do you think the fan could be blowing too much air down, not allowing enough out the exhaust fans?

Any help would be much appreciated. Let me know if this is impossible to picture without a visual and I'll try to take a pic later and post it if needed.

Thanks

Yes a pic would definitely help.

its totally common sense and you are over looking it. The circulation fan is blowing hot air down and forcing cool air up and out through the exhaust. Move the circulation fan to blow at canopy height and you should see a difference. the hot air will be allowed to rise and therefore be sucked out.

you must al ways remember
hot air rises
your exaust fan should be ontop
your circulation fan should be
@ a low level blowing the cool air upwards.
cooling the plants first,then lights,then exaust

*its not a good idea to have blowing
downward onto your plants
hope this was helpfull

Thanks guys. I'll try moving the circulation fan down to a lower spot.

Might have to go get a smaller one as this 8" Honeywell takes up some space. Securing it up top just seemed like the best spot in the box.
Common sense has failed me!
Thanks chasmtz & ksimon21
I'll report back soon, with pics this time

This is how the box looks. Big fan blowing down, and exhause on either side.

I'm taking out the fan on top as we speak... Going to look for something a little smaller to go on the side

mblue,
If you can remote mount your ballast above your fan, it will help with the heat making it out your exhaust. BTW, your thermometer position isn't giving you an accurate reading. It should be at canopy height.

I actually don't see the ballast in the picture but if it is in there, move it out side of the box if you can. Mount it on the back or something. Raise that thermometer too.