Ventilation problems please help

I have no clue what is wrong..

I just built a small cab 4ftX2ft. And 3ft tall.

I have a 250watt MH (attached to ballast) and the temps get to 90 deg.

I have a 6" axial fan pulling air from right under the bulb and blowing it outside. There is also a desk fan for circulation.

My ambient room temp is 80..
The thing that has me so confused is that I set up a temporary area in my closet with ONLY a desk circulation fan; no real exhaust or intake. Same 250 light (I have two). It stays the same temp!!

So how can a closet spot with no ventilation have the same temp as a cab with vent? Both are in the same room..

I really don't want to have to hook up AC just to veg..

Thanks

-Frozenguy


EDIT:

So I've been searching and it seems its kind of controversial as to whether or not the size of a room/grow box matters for cooling if the same size light is used..

I also found the formula saying that (3.16*total watts)/difference in temp = CFM needed to maintain that difference (from ambient).

I'm running 1 449 CFM fan and with 500 watts (250 light, 250 ballast) its like 1580cfm needed. I decided after the bends and turns, that i'm only getting 250CFM and that says I should get just above 6 deg difference which is what i'm experiencing now.. (I rearranged the ducting and got my "out" temp (hanging probe) to be 86).. My ambient room temp right now is around 81 deg.

Again, the air is vented to the outside of the house, out the window.

If you're within 5º using an axial, that's pretty good. Are you using dual 6" intakes? Try putting the ballast outside the cab.

Ventilation 101

I need to like, set aside some time to read that through..

I have fiddled around with it. This is my first time working in a cab and its proving to be a challenge.

The 6" fan is just sitting on the top of the cab sucking air up (no ducting anymore inside the cab, just a hole at the top for the fan..) and into a ~ 4"-5" ducting (need to pick up 6" obviously)..

That ducting goes out the window. I toyed around with different intakes but right now I have two intakes,at adjacent corners. One is 6" and the other is 4" right now. Once I cut the second one to 6" the temp started rising, so I put back the cut out part (this is cardboard LOL) and thats what i have right now. I'm testing it again to see what the temps get to and I'll try taking out that cut out piece to make it 6" again for both and see what that does..

~Frozenguy

Frozenguy said:

I'm running 1 449 CFM fan and with 500 watts (250 light, 250 ballast) its like 1580cfm needed.

Click to expand...

Not sure if we are talking about the same thing but your light only counts as 250w in that example if it's a 250w light. Unless you mean your fan is 250w as well.

ScrubNinja said:

Not sure if we are talking about the same thing but your light only counts as 250w in that example if it's a 250w light. Unless you mean your fan is 250w as well.

Click to expand...

I thought I've read that you have to count the ballast as a heat source AND the light bulb as a heat source since they both produce heat.. But I thought it sounded funny that there can be more then 250 watts of heat.. Can there be?

Ok so I'm just going to hook up my portable AC unit. Its 10000 BTU lol.. Should I put this inside the cab or outside the cab?

If I put it inside the cab, it will directly cool the cab. But the cab's exhaust will just throw the AC air outside the window and waste it. So maybe I can turn my fan off and only exhaust every 15 min/30 min?

If I put the AC in my room, the fan will still suck air out fast but it seems like the AC would be on all the time to keep the room up to temp..

What if I start exhausting the Cab just into my room? (the cab is in my room).. The AC should be able to handle that right? Then I can jus AC my room and not the cab directly.