Different Types of Greenhouse Fans – Which is Right for You?

Why You Need A Greenhouse Fan

Fans will help you break up air stratification. So you can expect hot air to get stuck in the top of your greenhouse, cooler air to settle down below, and these layers stay stagnant—stratified—unless your fans to break them up. 

In addition to temperature regulation, your plants will benefit from good air circulation because it assists photosynthesis. Fresh air moving through your greenhouse brings plants the carbon dioxide they need—which means it is also important to set up your vents and fans so that all plants are getting good airflow and available carbon dioxide. 

Occasional breezes also help plants grow strong and sturdy. Good greenhouse ventilation and airflow will even help pollinating plants…pollinate! The right types of greenhouse fans can seriously aid in this process.

Perhaps the most popular kind of fan, exhaust fans work by creating a pressure differential between inside the greenhouse and the outside world.

Exhaust fans don’t work alone: they function in conjunction with shutters or vents placed on the opposite side of a greenhouse. As warm air is pulled out of the greenhouse through the exhaust fan, the negative pressure inside the house pulls new air in through vents on the opposing side of the structure. Ahh, a nice, fresh breeze! 

Exhaust fans are fantastic at decreasing humidity, too.

Exhaust fans look like a big metal box with slats on the outside and a fan inside. Good-quality exhaust fans come with speed controllers so that you can adjust for your greenhouse size, plant needs, and climate. 

Circulation fans are those huge, metal-caged fans you’re probably used to seeing in commercial greenhouses. They can be mounted on ceiling rafters, frame posts, or even set on the floor. 

While circulation fans come in varying sizes and typically have a speed adjuster, they are less “nimble” than exhaust fans. Circulation fans are the bulldozer of greenhouse fans. They just blow—that’s all they know how to do.

But the benefit of a circulation fan is that it can provide a more “flexible” airflow pattern than a cross-breeze – similarly to an exhaust fan. That means you could place a circulation fan in a particular spot in your greenhouse that tends to get extra-hot, too cold, or too moist. They are perfect for getting air moving in tricky places and corners, breaking up air stratification.

Be careful when using circulation fans in addition to exhaust fans: circulation fans can mess with your carefully constructed exhaust-vent cross-breeze, as well as the natural airflow from greenhouse windows and vents. The best placement of circulation fans is in a zig-zag pattern.

If the air at the floor of your greenhouse tends to get stagnant or too wet, you may want a circulation floor fan. Ceiling-mounted circulation fans – like the image above – can get a little more pricey, but that’s what you’ll want if you’re utilizing circulation fans for all your greenhouse airflow needs.