1. circulation fan More Fans, Slower Speeds:  Rather than using just a few fans on high speed, add some extra wall fans and turn the speed down.  Air circulation is crucial to exchange CO2 at the leaf surfaces, but high winds can dry out or stress plants. You’re looking for Breezy, not Windy. 
  2. No Close-ups, Please:  Careful fan placement is crucial.  If wall fans are mounted too close to the canopy, wind burns and/or mechanical damage can occur as the canopy grows.  It only takes one stressed branch going hermaphrodite to ruin an otherwise perfect crop.  In tight corners or tents, using a smaller clip fan instead of a large one may fit better in the space or may be easier to mount in a better spot. 
  3. The Floor Fan Alley-Oop:  In gardens with CO2 enrichment, the heavier-than-air CO2 will want to settle near the bottom of the space.  Place a small floor fan like the Air King 9” pivot fan pointed upwards directly underneath your wall fans to lift and stratify the CO2-rich air at floor level.
  4. Clean ‘em Like Your Garden Depends on It:  Because it does.  Clean fans after every crop - more often if you have any fungal problems like powdery mildew present.  Ideally, you’ll want to clean your fans any time you spray for mildew control to prevent spores on the fans from being blown back onto your crop.  Disassemble the fan guards and remove the blades.  Spray with isopropyl alcohol and wipe each part completely clean.  This is the ounce of prevention that is truly worth a pound of cure.
  5. Keep Air Moving Under Tables and Trays.  Fans like the Quest F9 Industrial Air Mover are great at moving a lot of air under your tables and trays.  This helps even out CO2 disbursement in the room and keeps your floors nice and dry, particularly in rooms with long runs of benching.
  6. V-Flow Fans:  Used in commercial greenhouses, Vosterman’s V-Flow fans are ceiling mounted circulation fans that are awesome for large grow rooms and greenhouses.  They create a vertical ventilation effect in the center areas of larger spaces, pulling air up and then distributing it laterally.  If you’ve got a big expanse of canopy, these are the best overhead fans for air movement throughout your crop.