Simple way: cut a bunch of holes in the top! The heat will rise and your temps will be very close to the ambient room temp.

Mike

42.5 CFM means it should clear your tent of all the air in one minute provided you have an intake vent at the bottom and the fan on top. If you don't have a pre-made hole at the top then I would cut one there as heat rises. CFM stands for cubic feet per minute and by my calculation your tent is 40 cubic feet. To keep your tent at a constant temp you would need to set the fan up on a thermostat.
Any venting will drop humidity at least slightly and plants may go into shock but better than them all dieing.

Thanks for the info, both of you. I already have two 6'' holes at the top of the tent which were pre-installed. Those are always open because yes heat does rise ! I have been doing research on how to hook a fan up to a thermostat, taz, and I haven't found a whole lot of info about it that I can understand. Could you give me a walkthrough on how to hook one up?? Would it be possible to use a computer fan?? I have found some which are the correct size (4'') but have no idea if they would hook up to a thermostat.

Why not just have the fan run on the same timer as the lights?

I have a 400-watt HPS in a space that is about 3.5'x3' with Mylar on the back and side walls. Earlier this year, I covered the front of the area with a thick sheet (was experimenting with adding CO2) but the entire top was open. The temps stayed very close to the ambient air ones.

Mike

I like Mikes idea. You wouldn't need the fan when the lights are off.

Hey ethnobotony, I already responded to this on the hydroponic forum, but I'll do it again in case you haven't seen it. If you have a home depot near you, they sell 6" inline exhaust fan's for around $30. If you have a tent like mine, the exhaust ports will fit a 6" inline fan perfect. There's a draw string to tighten it up. I would do what taz said and buy 2, one for intake and one for exhaust. If you want it cool in your tent, get a 6" to 4" metal duct reducer and hook a dryer hose up to your intake. Duct tape the other side to your air conditioning register. Or you can buy a 12" square register to 4" reducer for a tighter fit. Everything you need will be in the air ducting isle. I have a 5'x5' grow tent and it works great.

One more thing. You can control the humidity by these steps:

1.To raise and lower the humidity, leave the intake on and the exhaust on a humidistat. Hope this helps.

Sounds like a good idea but my AC is a wall unit! Haha, sad but true.

Why do you need a tent at all? I assume this is indoors. My grow room (now dormant) consisted of a 1000-watt grow light suspended from the ceiling, a couple of white walls, a reflective room divider, and a window fan. No air got trapped, and I could adjust the fan to keep temps temperate year round.

I need a grow tent because I live in a studio apartment and attend college, which means I need rest. If I had no tent then the 18/6 light cycle would blind both my girlfriend and I's eyes at night. The tent isn't home-made, so I am definitely not going to tear it up since it cost me a decent amount of money. I already said there is 2 large 6'' holes at the top which will provide for ventilation but its not enough.

@ nygardener: yes, logically it makes sense that an actual room would provide a better environment for temperature control but due to my circumstances that is not an option.

I am wondering what cfm rating I will need to keep my temp down about 10 degrees. Any ideas? Likesay the grow room is 48"(L) x 24"(W) x 60"(H)(4ft x 2ft x 5ft).

In the mean time I have borrowed my gf's parents' weak tower fan which I hung up to the top of the tent using some kindof picture wire I had lyaing around (lol). With that in there the temp stays about 79-81 but it still isn't optimal. ESPECIALLY since the humidity stays very low at the current average temp.