I've had good results with (a) small computer fans I pick up at a local surplus store (one of them has the "Boxer" label on it); or (b) small table "personal" fans I found at Walmart. By "small" I mean around 3.5 to 4.00" diameter. The Walmart model in link.

Both types provide a gentle breeze.

Gary

http://www.walmart.com/ip/4-Mini-Personal-Fan-Black/34136721

How do you power the computer cooling fans and how did you mount them? Do you use an external control that allows you to change the speed?

I guess it really depends a lot on your lights and how much air you want or need to move. I use T5HO lights and like to keep them as close to the plant as possible. I also like to keep my growing temps down around 16-18C (61-65F) so need to move a lot of air. I, too, have a large fan that always seems to be in the way but it is the only thing that moves enough air without having a large number of smaller fans. I also have my fan(s) on a timer with my lights.

Have a great day,

SCG

I have three 4-bulb T5 basic fluorescent light fixtures hanging from my joists on retractable carabiners. I used to have a pricey 2-foot grow light but then came to the conclusion that it produced results no different than my cheapy lights from Lowes. Below are some pics of my setup from last year. I'll be eliminating the two foot grow light next to the treadmill and selling it. My idea of providing cross ventilation this year right now is to hang small clip-on fans that oscillate from the joists (angled downwards). This way my large fan from last year is not in my way.

IMHO, you are not going to gain anything from having fans up high angled down unless they are unleashing a fury of air! The way you have it set up now is, IMO, great. With the fan blowing between the lights and plants dispersing the heat, especially when the plants get bigger.

Cheers,

SCG

What is the supposed issue with oscillating fans? Use them all the time in the greenhouse with great results.

In any case I decided to move things around in my setup last night to compensate for loss of heat and loss of lighting in my previous setup. All my flats are up against a common wall now instead of being in the middle of the room. I am planning on adding three Zippi non-oscillating fans (all will be set to LOW and connected to a timer set on RANDOM - simulating a random outdoor breeze) to provide cross ventilation. In the photos below you can see the proposed location of all three fans (but only one fan is pictured). In addition I will be adding reflective white panels against the walls (only one pictured for now) so that any light that would normally be absorbed by the wall will be reflected back onto the plants. Does anyone see a flaw in my setup that I haven't considered?

@digdirt I don't think he had an issue with the fan just it was more cumbersome because it was in the way.

@njitgrad each to their own but for ME those fans are just not big enough. While much cooler than other lights T5's do put out a lot of heat. At the moment I am running 6 T5HO bulbs in a 10' X 13' insulated grow room in my unheated shop. I have a large fan, about twice the size of the one on your chair, on low blowing between my seedlings and lights.Those lights produce enough heat to keep the room at 19-22C (69-74F) which is above my intended temp of 16-17C (61-63F). Even with our outside temps dropping below freezing (28) at night and being slightly over during the day (36F). I have to open windows to lower the temp and my fan is thermostatically controlled to come on when the temp rises under the lights above 18C. Later in the year when the temps rise and I am running all my lights I have to run an air conditioner to keep temps down. It is quite possible I am being overly anal, but why not!!

I will also add that I move plants that like it a bit warmer out of the direct fan breeze and temps go up fast.

Not saying your set up won't work as it will and will do so well, it is just what you want. Moving lots of air lets me keep my lights closer, around 1" away, which I find better. YMMV.

Reflective material around the sides isn't as important with overhead fluorescents as it is with, say HPS. With HPS you have to keep the lights farther away to avoid scorching the plants so you benefit from reflective sides. With the overhead fluorescent lights only being inches away very little light is being lost out the sides to reflect back. I put mylar on the sides of one light and had zero increase in lumens according to a light meter. Again YMMV.

SCG