A greenhouse needs proper cooling and ventilation in every season. Even on cold winter days, the heat that gets trapped inside of a greenhouse can reach temperatures that might kill or injure your plants. So you need fans--but what fan should you choose? I'll lay out & explain the choices you have when it comes to greenhouse fans, and I'll recommend a few products based on your needs and budget.
My Pick: The J&D Industrial 14" Fan
Choosing which fans to use in your greenhouse can feel complicated and overwhelming. There are a ton of different types of fans, as well as premium brands and features to sort through. My overall recommendation is the J&D 14" fan. It comes in several different sizes (not just 14"), is simple and affordable--while still having everything you need.
You can find your favorite size of the J&D Industrial fan online from several affordable sellers, including Amazon, Global Industrial, and Valley Vet Supply. This model is incredibly versatile and efficient.
It can be used in so many ways, from adding ventilation to a chicken coop or--as in this case--cooling your greenhouse. The J&D Industrial fan can be mounted on the wall or easily hung from the ceiling.
I love this because it simplifies the decision making process so much! I know that I can use this same fan in any placement in a greenhouse (or a barn or a chicken coop), rather than purchasing separate and more expensive fans for different placements.
Can’t beat that simplicity!
This J&D fan comes in larger and more powerful sizes too (18" and 24"). There are even bigger ones as well, but those fans aren't as versatile (i.e. they can only be mounted one way).
If you are anything like me and math is your long-standing arch-nemesis, this easy breakdown is for you: the plants (and humans) in your greenhouse need to breathe healthy air. Fans move air and keep it healthy.
But how are you supposed to know how big of a fan you need to ventilate your space?
Fans are measured in something called "CFM", which stands for "Cubic Feet per Minute". CFM refers to the volume of air that is being moved (per minute) by the fan in your space. You will want a fan that moves a volume of air equal to or greater than the cubic feet in your greenhouse. A helpful way to picture this is: one CFM generates approximately two litres of air per second.
But what is a cubic foot? It's the length x width x height of the area. So for example, let's say you have a standard sized 10x12 hobby greenhouse with an 8 foot ceiling height. You'll multiply all three dimensions (10x12x8) and you have the cubic feet of your greenhouse--960 cubic feet.
If the cubic feet equals 960, and the CFM capacity of your fan is also 960, then you would be cycling the entire volume of air through the greenhouse in one minute. In equation form, that is to say that:
960 cu. ft. / 960 CFM = one minute for the fan to cycle all the air in the room.
The J&D 14" fan is an ideal size for a greenhouse like the example above, with the capacity to move air at 1,090 cubic feet per minute--plenty of power for the small greenhouse. The larger your greenhouse is, the more CFM capacity you will need. You will need to work out how many fans it will take to handle the volume of air based on the cubic feet of your greenhouse structure.
Geez! I'm glad the math part is over. I guess I should have paid more attention in 4th grade?
It's important to note that from the position of this article, I am assuming that you will already have a plan for natural ventilation systems in your greenhouse. Natural ventilation refers to vents, louvers, open walls, open roofs--etcetera--that let air in and out of the greenhouse structure. These systems can be operated manually or mechanically, and are crucial for good ventilation. A fan is not going to do you any good if there is nowhere for it to push the hot air out of, and draw new air in.
Where should I put my fans?
The most common placement is to have your fan (or fans) in front of the wall at one end of the greenhouse, blowing air towards the vents or louvers on the opposite wall. If the length is more than 150 feet, you should install fans in the mid range of the greenhouse as well (40-50 feet apart from the first ones) to help the air move toward the vents.
You also want to make sure that the fans are moving the air above your plants and in the upper space of the canopy. Hot air rises, so it won't do you any good to have fans that only move air on the ground. Install all your wall vents and fans to operate at least 2 to 3 feet above the plants.
Types of Fans
There are 3 main types of fans relevant to greenhouses. HAF fans, Vertical Circulation fans, and exhaust fans.
HAF fans, or Horizontal Air Flow fans, are the kind that we've been talking about in this article. The J&D Industrial fan I recommended is an HAF fan. Horizontal Air Flow fan systems are a God-send to the greenhouse growing world, making it possible for us to maintain an even temperature throughout the entire greenhouse--when properly installed.
So what are they?
Horizontal Air Flow (HAF) fans
Horizontal Air Flow (HAF) fan systems are fans that blow air horizontally. Duh. But more specifically, it refers to the use of a group of fans (the fan system) spaced far enough apart in a greenhouse structure to keep the air moving horizontally throughout the whole thing. Air is heavy, and by using multiple HAF fans, you can create enough power and force to lift the heavy air and keep it moving.
In an HAF system for a larger greenhouse, you want the total CFM capacity of your HAF system to be 2x the cubic feet of the greenhouse.
So if your greenhouse is large, say 30x100 feet, you would definitely want to use an HAF fan system.
If you place them 40-50 feet apart in the same way I described earlier--you would only need 4 fans--which is enough power to cover the 6000 cfm (30x100x2).
Vertical Air Flow fan
The next type of fan is the Vertical Circulation fan, or Vertical Air Flow fan. This is basically a ceiling fan and it operates the same way. It's suspended from the ceiling so that the vertical air flow pushes down any hot air that is sitting or getting trapped at the top of the greenhouse. This regulates humidity and results in more even plant growth.
A vertical circulation fan may not be necessary in smaller hobby greenhouses. In fact, to accomplish vertical air flow in a small greenhouse, I would recommend simply using a second J&D 14" fan, hanging it from the ceiling (either in the corner, or in the middle of the greenhouse) and tilting the fan to face downwards.
Then there are exhaust fans. An exhaust fan is what you have over your stove to draw smoke filled air out of your kitchen when you burn dinner. The same concept is helpful in a greenhouse (although I really hope nothing is burning there).
There are all kinds of great product options for exhaust fans on Amazon, like the Fantech 2SHE1221 Series 12" Shutter Mount Exhaust Fan. This fan would be installed in the wall opposite the HAF fan(s). The HAF fans blow air toward the exhaust fan(s), and the exhaust fan sucks that air in and spits it out of the greenhouse through its vents.
How to choose a fan type
So how do I know which fans I need? Good question.
The smaller the greenhouse, the fewer fans and types of fans you will need. The larger the greenhouse, the more fans you will need, simply because you need more air flow variation to keep things balanced.
In a small, hobby greenhouse (like the 10x12 mentioned earlier), you can get away with one or two HAF fans (like the J&D), and some natural ventilation (vents/louvers). Since the greenhouse is so small, you could operate this system manually and keep costs down. Exhaust fans would be helpful here too, but not entirely necessary if your natural systems are efficient.
In larger greenhouses, you need more air flow variation simply because you have more air and that air is heavier to move around. For optimal temperature regulation in these structures you will want to use all three types of fans: an HAF system, exhaust system, and vertical circulation system. A bigger greenhouse has a lot more places for air to get trapped, and requires a lot more power to move the volume of air it contains.
Remember to do your own CFM calculations to make sure you are buying enough fans to handle the volume of air that your greenhouse holds.
Other Options and How They Compare
The J&D fan is an awesome choice for medium/lower budget, but there are some even cheaper options. If money is super tight, or you don't have the budget to buy multiple J&D fans, look for the Comfort Zone 18" High Velocity Industrial 3-Speed fan. As of September 2019, this fan can be purchased at Home Depot for only $46 US dollars, half the cost of the J&D.
If you have a higher budget and want something higher quality with greater strength and load capacity, look for Twister Fixed Circulation Fans from Schaefer Ventilation. Prices vary as there are several different models to choose from, and prices are disclosed via private inquiry between you and Schaefer Ventilation.
What does it cost to operate my fan?
The average operating cost for one small fan is about $0.25/day at 10 cents per kilowatt (a "small" fan is a fan between 12" and 24" in diameter). If you have four 18" fans, estimate $1 per day to keep them running.
Maintaining your fans well will help keep your energy costs down. Clean your fans and fan blades regularly to keep them running efficiently. Make sure your fans are mounted securely so that the force of air doesn't shift them around. And of course, making sure that you are using natural ventilation whenever possible will cut down on electricity costs.
If you want to get even more serious about cutting electricity costs, there are some viable solar options you may want to investigate. Though they come with a higher up-front price tag, solar powered ventilation systems will save you thousands of dollars in operation costs. These fans are definitely worth looking into if you have the budget for it and if you are invested in the future of sustainable agriculture. Snap-Fan is a California based manufacturer of solar powered ventilation systems--you should check it out!
What To Avoid
At first glance, fans seem way too simple to have much variation in quality, right? Wrong. Fans ARE very simple (albeit genius), but they are not all created equal.
Cheap and crappy materials are the top things to avoid when purchasing a fan for your greenhouse! Read the specs and the reviews of the fan before you purchase it. Usually, if it's made of low quality materials, customers will be complaining in the comment section about broken pieces or weak airflow.
The heavier the material, the stronger (and usually safer) the fan. Fans made of galvanized steel can be small, but still way more powerful than many of their plastic or synthetic counterparts because their blades are thick and efficient. That is not to say that all plastic fans are bad, but many are, so look carefully!
What to look for
Fans come with a lot of “cool” features these days (pun very much intended). Not all of them are necessary for everyone, but you should know what your options are.
First and foremost--look for features that make your fan user friendly. From assembly to operation, you want to be able to manage this fan on your own with minimal time involved. You’re buying a fan, not having a child--you don’t need to labor over it and babysit it. Read the details and reviews of the fan to figure out how much it weighs, assembly and mounting instructions, etcetera, to make sure you can manage it.
Another important thing to look for if you value having a social life at all, is any feature that allows you to operate hands-off or even remotely. A lot of fans come with remotes, programmable timers, and digital controls. These things give you the freedom to go places and do things without being worried about getting home at a certain time to turn fans off or on.
Best Greenhouse Fan Round-up
So let’s just do a quick round-up of the products I am most comfortable recommending to you, based on your needs and budget.
- For a lower budget/smaller greenhouse I recommend the Comfort Zone 18” High Velocity Industrial fan. It has 3 speeds, can be mounted and tilted various ways, has 1,470 CFM capacity, and can be purchased on Home Depot’s website for $46 US Dollars.
- For a medium budget my recommendation is the J&D Industrial 14” fan. It comes in multiple sizes, boasts excellent versatility, has 1,090 CFM capacity, and can be purchased from many online sellers, the most expensive of which sells it for $100 US Dollars.
- For a higher medium budget, look for Schaefer VersaKool Circulation Fans. There are different models and sizes of this fan, starting at $205 US dollars. These are the epitome of powerful and durable. Made with galvanized steel and a deep cage, this is one of the most powerful and still “affordable” industrial fans out there.
- For a high budget, look for Twister Fixed Circulation Fans (also from Schaefer Ventilation). Schaefer is definitely a top dog in the industrial ventilation game. Quality, powerful products worth every penny--if you have that many pennies. The Twister Fixed models do not have prices listed--you have to send an inquiry to the company to receive a quote.
- Also for a higher budget I really want to recommend solar powered fan systems, like the ones from Snap-Fans. If you have the financial ability to invest in something that is eco-friendly and sustainable--please do!
My pick for best overall is the J&D Industrial 14” fan. I chose this because of its affordability and versatility. Many of you are probably looking to set up smaller, hobby sized greenhouses and you don’t need a monster fan. Yet, you still want something that'll last, as well as the financial ability to have multiple fans. Because it's under $100 US dollars, and has ideal hobby farm versatility--my top recommendation is this J&D 14” Industrial fan.