By GanjaGuru at MP

Ventilation How-To
Many years ago, when I first set-up an indoor grow, I did some reading up and had adequate light, good soil, good nutrients.
I asked an experienced indoor gardener what I was missing.
What was the missing link to high yields of quality ganja in a timely fashion?
One word.
"Ventilation."
I thought to myself "yeah sure what does he know?"
Turns out, quite a lot.
Flo-thro ventilation is the missing link to optimum conditions.
Tempeture control is 1 reason, but there's an equally important reason.
With NO fresh air, you will barely be able to grow.
Plants "eat" CO2 (and "exhale" oxygen). With CO2 is used up, growth stops.
So you don't just need a little fresh air, you need lots.

Closets/Wardrobes
If you are renting, or simply don't want to damage your closet door, replace it with a cheap-o used door. You can pick one up at a home dismantlers or a new one at homedepot, etc.
Or simply cut-to-fit a piece of plywood.
Also pick up 2 bathroom exhaust-type fans (under $15.00 each), and 2 plugs. If you're using plywood you'll need hinges and a handle.

Tools
You will need a drill with a large bit for a pilot hole, saber or hole saw and a screwdriver.
Also some electrical tape and wire nuts.

Using the template provided, cut 2 holes. I up as high as possible (the ceiling is ideal). That is the exhaust. Cut the other as low as possible (intake). The top fan faces out, the lower one faces in. Install the fans securely.
Wire the plugs and you're ready to rock. Plug 'em into your power strip and leave them on full-time.

Now you have a problem with light transfer. You don't want this. It can be dealt with in a number of ways.
One way is to attach a piece of "S" shape piece of ducting the same diameter as the hole. Spray paint the inside of the ducting flat black.
Or you can try to locate the hole behind a desk, etc. (allowing enough clearance for free air flow). I once fashioned a cardboard baffle near the ceiling to block light transfer.

These 2 fans will provide adequate ventilation for most closets.
For larger area's you may need more powerful fans.
Determine the cubic feet of your growspace (l x w x height). Then shop for fans. How much air fans move is rated in cf/m (cubic feet per minute). You want one that equals or surpasses your growroom cubic feet.
For bigger spaces, you may want to upgrade to squirrel-cage fans. In-line fans are the best (and most expensive).

And finally you need an oscillating fan inside the growspace on a shelf (or clip-on) for air distribution and stem strength.

The difference between poor ventilation and excellent flo-thro ventilation will surprize you.