Why Horizontal Air Flow is Important

st popular horizontal airflow fan (HAF) systems involve circulation fans which are often set up to flow air in a horizontal pattern. The concept is that air in a space only needs enough energy to overcome friction loss and turbulence to keep air “moving along." The circulatory fans and other equipment mixes warm air from the upper region of the greenhouse with cool air below, the thermal buoyancy effect is lost, and temperatures are more consistent.

Horizontal airflow is the gold standard for greenhouse air circulation. There are a surprising number of benefits to HAF. Moving air removes moisture from the canopy, strengthens stalks and stems, replaces carbon dioxide depleted air during daylight photosynthesis, and helps maintain uniform conditions in the greenhouse.

HAF greenhouse ventilation

Benefits of Horizontal Air Flow

  • Mixes the air to provide more even temperature with as little as 2°F difference between any two points in the greenhouse. 
  • Greenhouses that use fogging to apply pesticides will see more even fog coverage and better penetration of foliage when used with a horizontal airflow system.
  • HAF fan operating cost depends on electricity rates, at a rate of $0.10 per kilowatt-hour, they can cost as little as $0.24 per day.

Greenhouse HAF Fans For Sale

EZ-Breeze HAF 20" Basket Fan

haf fan for circulatory airflow

J&D Manufacturing’s EZ-Breeze HAF (Horizontal Air Flow) Fan is a high-efficiency air circulator. This type of fan is good for cooling plants and reducing condensation. These HAF greenhouse fans also help create a uniform temperature throughout your building to reduce heating costs.


  • Available in 12”, 16”, 20” and 24”
  • Includes corrosion resistant hot dip galvanized mounting bracket with u-bolts and nuts
  • Aluminum propeller designed to reduce ambient noise levels while maintaining maximum circulation requirements
  • Efficient variable speed motors (requires separate variable speed control to adjust fan speed)
  • Corrosion-resistant, white powder-coated fan guards meet OSHA 1910.212(a)(5) requirements for installation at any height
  • Attached 10’ cord with 3-prong plug pre-wired for 115 volts
  • Totally enclosed, maintenance-free, direct drive high-efficiency motors have completely sealed ball bearings, are UL/CUL recognized, and are covered by a Two Year Warranty
  • For additional cooling, use with our misting/fogging product line
  • Single-phase

A Deeper Look: Horizontal Airflow Fans for Greenhouses

Solar radiation on warm spring and fall days can increase leaf temperatures ~15°F higher than the air temperature and result in burnt leaves, flowers, and fruit. Horizontal airflow removes much of this excess heat and protects plants from the damages of excessive heat. The heat disperses quickly from one end of the greenhouse to another.

Horizontal airflow also helps prevent the formation of condensation that can harbor pathogens because when air moves at a rate of 50-100 feet per minute, leaf and air temperature at night have little difference. When there is not a significant temperature difference, condensation will not form so readily. 

In order to push air with just enough force, fans must be properly sized and placed. Air is actually quite heavy, the air above one square foot of greenhouse floor weighs about 1 lb. or 1.5 tons of air in a 30 x 100-foot greenhouse space! Four small fans with proper placement for horizontal airflow can keep that heavy air moving up to 50-100 feet per minute when properly placed for horizontal airflow, making it a high-efficiency ventilation method.

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