Table of Contents
- 1 How to Choose the Right Inline Fan?
- 2 What is CFM?
- 3 Calculating CFM
- 4 Inline Fans
How to Choose the Right Inline Fan?
Anyone who’s ever been to a hydroponics shop can tell you that purchasing the right equipment is just as tedious and arbitrary as choosing a shampoo at your local department store. You might have a general idea of what you’re looking for, but you’ll also be bombarded with tons of variations of essentially the same product, most of which do the exact same thing. Whether it’s a 6-inch inline fan, exhaust fan, or vent fan, you’ll most likely end up relying on the recommendations of your hydroponics shop, and you may end up paying way more than what you should have, even for something you really didn’t need in the first place.
We know the struggle. But before we can tell you what to buy, you’ll have to know exactly what it is you’re looking for. And to figure it out, you’ll need a basic understanding of how air circulation works.
What is CFM?
Every fan, whether it’s a 6-inch inline exhaust fan or an extractor fan, has a CFM rating, which stands for “Cubic Feet per Minute.” This is basically the amount of cubic feet of air that the fan can move in a minute. Some growers tend to ignore CFM ratings because the primary function of inline fans is to dissipate heat, but that’s only part of what they’re intended to do.
Understanding Plant Biology
On the leaves of your plants, there are tiny pores called stomata (wikipedia link – opens in new window), which are essentially the breathing points of your plants. The stomata on the leaves function as a way for the plant to absorb CO2 and oxygen while dispersing water vapor as a waste product in a process called transpiration, at which point the plant will draw more water from the roots. The stomata will behave according to the conditions of the plant and its surroundings.
With a bright light and enough moisture available through the roots, the stomata will become dilated, allowing for more CO2 and oxygen to be absorbed. As the soil becomes dry, the stomata will close to preserve water, thereby halting photosynthesis. With too much water (overwatering) the stomata will dilate to release as much water vapor as possible, but at a rate that can be dangerous to the plant’s survival and development.
What does all this have to do with inline fans?
As the stomata releases water vapor as a waste product, this waste must be displaced from the grow room via inline fans. If you don’t extract enough air, the air will become thick with water vapor, your plants will have less access to essential CO2 and oxygen, and photosynthesis will be disrupted. However, if you extract too much air, you’ll also be extracting all the precious CO2 that your plants need to thrive.
Simply put, you need to use your inline fans correctly to find the sweet spot for your air circulation.
This allows the plant to absorb all the CO2 it can while also transpiring excess water vapor. If you base your sweet spot around three minutes, the rest of your calculations will involve basic math.
Let’s take, for example, a 10’x10’x12’ room. We need to find the cubic feet of the grow tent, which is expressed by multiplying the length, width, and height:
10 x 10 x 12 = 1200 cubic feet
That’s the amount of air we need to displace every three minutes. But since fans are calculated per minute, we need to divide our cubic feet by three to find out how much cubic feet of air we need to displace per minute, which will be our ideal CFM:
1200/3 = 400 CFM
So, for a 10’x10’x12’ room, we know that we need a single 400 CFM fan to extract all the air within three minutes. Although this doesn’t take into account various turns in your ducting that slightly restrict airflow or intake fans that you may have pushing fresh air into your grow space, this is generally going to be in the ballpark of what you’re looking for in your fans.
Now that you have a better understanding of CFM ratings, check out this comparison of various 6-inch inline fans on the market:
|Atmosphere S-600 Vortex S-Line Ultra Quiet 6” Inline Fan||347||$$$|
|Can Max Fan Mixed Flow 6” Inline Fan||334||$$$|
|Active Air 6” Inline Fan||400||$$||🙂|
|Hurricane 6” Inline Fan||435||$$|
|Yescom HO 353||353||$$|
|VenTech VT DF-6||240||$||🙁|
|iPower Grow Tent Ventilation SET (Filter and Duct Included)||442||$$$|
Atmosphere S-600 Vortex S-Line Ultra Quiet 6” Inline Fan
- 347 CFM
- 66 Watts
- Double Insulated Wall for Noise and Humidity Reduction
- Quick-Removal Clipping System
At first glance, the Vortex S-600 seems like a beast of a machine. A superior build quality and fancy design will certainly turn some heads in your grow room, and may even justify its price tag. But don’t be fooled. You won’t get much more out of the S-600 than most other fans on the market, and despite Vortex’s claims that this is an “ultra quiet” fan, the S-600 is pretty loud. If you’re looking for a quiet inline fan with a decent price tag, look elsewhere.
Can Max Fan Mixed Flow 6” Inline Fan
- 334 CFM
- 75 Watts
- Plastic housing
- Mixed Flow Blade Design
Can Fans are very popular these days, and for good reason. They’re relatively light, small, and sturdy. In addition to great design, the Mixed Flow 3-speed controller allows you to switch the speed to meet your growing needs, so you’ll actually be saving power if you don’t always need it to be running at full blast. Of course, if you’re getting a 334 CFM fan when you only need half that, you might as well get a 4-inch inline fan instead.
Active Air 6” Inline Fan
- 400 CFM
- Metal Housing
- Durable Ceramic Coating
- Mounting brackets included
Say what you want about Active Air inflating their CFM numbers, but if you’re looking for a fan that does what it intends to do, Active Air’s 6” Inline Fan certainly does the job. It’s relatively quiet, and could even outperform some 8-inch inline fans on the market when it’s used correctly. The mounting brackets certainly help as well; mounting fans is always a pain, but the brackets make things a whole lot easier.
Hurricane 6” Inline Fan
- 435 CFM
- Steel Housing
- Powder coated finish
- Mounting Brackets Included
Hurricane fans are usually good investments, and their 6-inch 435 CFM model is no exception. The steel housing and coated finish certainly add to the quietness of the fan, and $90 for 435 CFM is certainly tempting when you’re looking for a competent fan for your grow space. The only problem with the fan is how the mounting brackets sit on the housing; you might have a hard time drilling the brackets in with how they’re seated against the housing. But that’s a minor concern for a top quality inline fan.
Yescom HO 353 CFM 6 inch fan
- 353 CFM
- Extended collar for ducting
- Moisture resistant
Yescom is a relatively unknown brand in the hydroponics air flow market, but names don’t mean much when you’re looking for fans anyway, especially when you consider that the Yescom claims 353 CFM for $65.95, which is far cheaper than a lot of other brands. Although we can’t promise the fan will be all that quiet, the design itself is pretty solid. The extended collar is similar to the Active Air, and should meet your air circulation needs just as well if you’re not worried about brand names.
VenTech VT DF-6 inch
$ – dirt cheap 🙂
- 240 CFM
- 37 watts
- All steel construction
- Powder coating
The VenTech may seem far inferior to the other fans we have listed here based on 240 CFM, but we couldn’t complain with a price tag of about 20 bucks. Granted, it won’t do much for an entire grow room, but if you’re running a stealth box grow with only a few plants, the VenTech VT DF-6 may be for you. It’s pretty loud, but you can’t expect much with such a low price tag. To be honest we do not recommend this fan.
iPower Set : 6Inch High CFM Inline Exhausting Fan + Carbon Filter + Duct Fan
- 442 CFM
- Metal fan blades
- 95 watts
- Carbon Filter and Ducting Included
It’s not always a good idea to buy fan and filter combos because you can generally find cheaper alternatives if you buy them separately, but the iPower package is a real deal. Considering you’re probably going to need charcoal filters and ducting anyway if you’re trying to run a 442 CFM fan, the iPower package could be saving you money. iPower is generally pretty consistent with most of their products, so you can bet the filter and ducting are going to be quality products. Big plus – Cotton Pre-Filter cover is included for your filter so you can increase the filter’s longevity.
Shopping for fans can be tough, but if you just do the math, you’ll know exactly what you need.
Written by Pete Treebumrung