Lately i have been answering a lot of questions about setting up a grow tent, particularly a lot of questions about how to get tempuratures dialed in and how to control odor. Instead of responding to each individual thread, i have decided to put my personal experience into one thread to help out. Now this is by no means the only way to get a tent to work properly but this is how i do it, how i have taught others to do it, and it has been extremely successful for myself and those i have assisted.
The example im going to use is a 4x4 tent with a 600w light. A close friend runs the same setup in 5x5 tents with 1000w lights and the only changes made are larger fans.
First off, dont try and use just one fan to cool the light and ventilate the tent. The light generates heat inside the tent, so if you are using air from inside the tent to cool the light, you are using air that has already been heated. This is horribly inefficient and makes controling temps very difficult. Use ducting and an air cooled hood to draw air from outside the tent, through the hood, and back outside the tent. If your using a 600w light all you need to acomplish this is a 6 inch booster fan (these can be found for $25 online).
Now for ventilation/odor control. Use a small carbon filter for odor control, they work wonders. In my tents i use filters that come with 4 inch flanges, these move plenty of air for a tent. You will need a "vortex" style inline fan to pull air through the filter, booster fans just dont have the balls. Mount the carbon filter to the very top of the tent - heat rises so extracting air from the top of the tent removes the most heat. Use ducting to vent the air from the filter out of the tent. I highly recommend a speed controller for this fan for 2 reason: 1) it gives you more control over the temps in your tent and 2) when at full blast even a 4 inch fan will pull the sides of your tent inwards quite a bit. Dialing the speed down slightly has the added advantage of reducing the sound considerably. You also need a small circulation fan inside the tent to keep fresh air passing over the leaves.
in this picture you can see the intake duct for the light and the exhaust duct from the carbon filter
in this picture you can see where the hot air from the light is exhausted. that fan movesplenty of air for a 600w light and short ducting.
in this picture you can see the carbon filter and fan.
this picture shows all the interior ducting
