Horizontal air-flow (HAF) fans are an important component of a greenhouse or high tunnel. HAF fans are used most often in greenhouses for internal air circulation to eliminate hot and cold spots, especially when you are utilizing gas heaters.
Even heat distribution increases heating efficiency and ensures more uniform temperatures throughout the structure. Horizontal air circulation within the structure also helps with disease suppression, by preventing moisture build-up on plants from creating spores that cause fungal diseases such as Botrytis.
Finally, the biggest benefits for high tunnel growers are when the HAF fans are running during the summer months, outside air that contains more CO2 is being introduced into the greenhouse. This typically results in greater crop yields. HAF fans are a small investment with an excellent ROI!
Here are some guidelines for selecting and setting up your HAF fans for maximum efficiency.
Fan Capacity and Sizing
Using adequate fan capacity will ensure that you avoid any hot or cold spots in your greenhouse microclimate. The number of fans will depend on the volume of the greenhouse space and what you are growing. We recommend two rows of fans – so four fans total in a 30 x 96 ft. greenhouse (2,880 sq. ft). If you are growing taller, thicker crops like tomatoes or cannabis, you may need more fans.
Here are some sample layouts for HAF fans in a single-bay or multi-bay greenhouse:
Rimol offers 12 in. and 20 in. variable speed fans . A 12 in. fan is recommended for greenhouses that need more control with air flow, and a 20 in. fan is recommended for larger greenhouses that need maximum air circulation.
Fan Spacing
It is important that you are spacing fans appropriately for optimal air movement. As a general guideline, one fan is required every 50 feet.
If fans are spaced too far apart, you may create a dead air cold spot. Smoke bombs, foggers, or even incense sticks can be used to test the air flow in your greenhouse. Once your fans have been set up and given some time to stabilize, place the smoke or fog behind one of the fans. Watch its movement to ensure adequate air movement.
Fan Mounting Location
Fans should be mounted above the crop canopy or along the sidewalls of your greenhouse. For greenhouses with floor or bench crops, mounting around 8’ up usually works well. If you have hanging baskets, position the fans at or below basket level for minimal resistance and to avoid drying out your flowers.
