Benefits

• Horizontal air flow fans help to control fungal diseases in greenhouses.Jupiterimages/Photos.com/Getty Images
  
  Greenhouses use horizontal air flow fans. When properly spaced and sized, these fans help to regulate temperatures within the greenhouse. They are an effective way to eliminate cold pockets in a greenhouse. These fans create a movement of air that helps to reduce the moisture in the canopy of greenhouses, which helps to reduce many fungal diseases of foliage in greenhouses.
  
  

When To Use

• Greenhouses heated by furnaces or boilers get some relief when horizontal air flow fans are operated.Comstock/Comstock/Getty Images
  
  Horizontal air flow fans should be used in a greenhouse when fungal diseases infect plants, when greenhouse air is noticeably stagnant or when temperatures and humidity throughout the greenhouse are noticeably different. They should also be used whenever greenhouses are heated to help distribute the warm air. The taller the greenhouse, the more the need for electric fans. In greenhouses that do not otherwise vent, horizontal air flow fans may be the only feasible method of air circulation.
  
  

Size Requirements/ Orientation

• For optimal performance, fans should be placed in opposing directions when using multiple fans.PhotoObjects.net/PhotoObjects.net/Getty Images
  
  To generate the full benefits of using fans in the greenhouse, use an adequate number of fans for the given space. Place fans 2 to 3 feet above the tops of the crops angled downward at a 10 to 15 degree angle. Place one fan per 40 feet of width. Horizontal air flow fans should be able to move 2 cubic feet of air per minute per each square foot of floor area.
  
  

Other Methods

• Perforated tubes should not be placed higher than 8 foot above the greenhouse floor.Jupiterimages/Photos.com/Getty Images
  
  Electric fans are the most common method for improving circulation in a greenhouse, but other methods are available. Using mesh-type open bottomed benches is an easy non-energy consuming method for improving air circulation around plants. Make sure that your plants have adequate spacing on the production tables to improve circulation and reduce instances of diseases.
  
  Some use perforated poly-tubes in lieu of fans. These plastic tubes have holes every 1 to 3 feet and are usually sited on the greenhouse floor. They should be capable of delivering the same volume of air as the horizontal air flow fans.