How To Choose The Best Inline Fan

Choosing the best inline fan is crucial for the health of your system.

• If you choose a fan that’s too small, your plants are at risk.
• If you choose a fan that’s too big, you’re wasting money.

Fortunately, it isn’t hard to figure out the size of the fan you need.

Unfortunately, there are a lot of cheap, knockoff fans masquerading as quality options. They advertise flow rates and performance you’re unlikely to observe, which jeopardizes your entire crop.

If you’re building an efficient grow room with grow lights, carbon filters, growth media, and nutrients, don’t waste your entire investment by choosing the wrong fan.

If you’re unsure which manufacturer makes the best inline fan, this guide is all you need.

What Is an Inline Fan?

Inline fans are mounted in the ductwork to ventilate a space without physically being in that space. That’s the inline part. They’re also called duct fans, inline duct fans, exhaust fans, and intake fans.

If you’re building a fully self-contained grow room, they’re a crucial part of your home grower setup. After all, you can’t just stick a traditional oscillating fan in a sealed grow tent and expect it to push air through your ductwork to properly ventilate your plants.

Choosing the best inline fan for your grow room, grow tent, grow cabinet, or other self-contained indoor grow space is hugely important and depends on several factors.

• Your grow room’s size
• How much heat your grow lights generate
• The climate where you live
• The specific place in your home where you’re growing
• The plants you’re growing and the conditions they prefer
• How much ductwork you’re using
• Whether you’re using an inline carbon filter

And a few more.

We’ll cover each in more detail below and explain exactly how to account for each when choosing the best inline fan for your setup.

Why Is Ventilation Necessary?

It’s hard to understate the importance of a proper air circulation system, and an inline fan for grow room ventilation is key. An active air circulation setup that routinely circulates air every 1-3 minutes is essential and impacts several key processes:

• Supply plants with ample CO2
• Regulate humidity for healthy plant respiration
• Remove excess heat generated by grow lights
• Control disease and pests, which love hot, humid, stagnant environments
• Strengthen plant stems through air currents generated by ventilation

Active air is critical for all of these processes. Plants grown outside get that active air from nature, but grow tents and grow rooms need mechanical intervention to ensure proper temperature and humidity. A fan with a mixed flow design provides that active air.

4 Common Inline Fan Sizes

There are four common inline fan sizes measured in diameter:

• 4 inches
• 6 inches
• 8 inches
• 10 inches

As a general rule, a larger fan diameter means more airflow. Which size is right for your setup? There are two factors:

1. The CFM rating of your fan
2. Your grow room’s volume

Let’s start with CFM.

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As a general rule, larger fans circulate more air. Which size is right for your setup? There are two factors:

1. The CFM rating of your fan
2. Your grow room’s volume

Let’s start with CFM.

CFM Is How You Measure Airflow

Airflow is the most important duct fan feature, and CFM (cubic feet per minute) is how you measure a fan’s ability to generate airflow.

Higher CFM ratings indicate an increased ability to move air, and that’s what allows it to ventilate grow rooms, HVAC exhaust systems, AV closets, or just cycle fresh air consistently during COVID 19.

For example, the AC Infinity Cloudline T6 is a 6-inch inline duct fan rated up to 402 CFM, which means it can move air at a rate of up to 402 cubic feet of air per minute. That’s more powerful than the 6-inch Vortex 347 CFM inline duct fan.

There are several factors that impact a fan’s CFM:

• Size
• Construction materials
• Design of the fan’s cylinder, blades, and propeller
• Motor power

Of those factors, size is the most important. Take these two fans from AC Infinity, for example:

• AC Infinity Cloudline T6: 6-inch diameter fan with 402 CFM
• AC Infinity Cloudline T4: 4-inch fan with 205 CFM

The T4 is just 33% smaller but it has 50% less airflow for significantly less air circulation.

The Purpose of This Guide

It’s impossible for one guide to the best inline fans to speak to everyone because everyone’s indoor setup is different.

Instead, I want to accomplish two things with this guide:

1. Cover the universal information that’s true for fans of all sizes.
2. Link to detailed guides for each fan size (4, 6, 8 and 10 inches) so you can learn more about the specific type of fan that’s right for you.

For starters, here are links to specific guides for each inline fan size. If you don’t know which size you need, keep reading below to figure it out.

Which Size Fan (And How Much CFM) Do You Need?

I already mentioned the two factors that dictate which size of inline fan you need: the fan’s CFM and your grow room volume.

CFM is covered above, so let’s talk about your grow room’s volume. Once again, there are two factors that matter:

1. The diameter of your ducting
2. Your grow room’s volume

Let’s look at each.

1. The diameter of your ducting

An inline fan sits in the ductwork, so it needs to match the rest of the components in the system.

If you have 6-inch ducts, you need a 6-inch fan.

2. Your grow room’s volume

Your inline duct fan needs to be powerful enough to recycle all of the air in your grow environment with fresh air at least once every three minutes—ideally, faster.

Because duct fans are measured in CFM (cubic feet per minute), it’s easy to calculate how much fan you need:

1. Measure the volume of your growing tent or room. You can probably find this in the spec list of the product, you can measure the dimensions and use your third-grade math skills. For example, a 5′ x 5′ x 6′ grow tent has a volume of 150 cubic feet.
2. Divide the volume by 3 to find the minimum CFM of your unit. In our example, a 5′ x 5′ x 6′ grow room requires a fan with at least 50 CFM (150 / 3).

Wait, 50 CFM? That’s it? You definitely don’t need a 6-inch fan with 350 CFM then, right?

Pump the breaks. We aren’t done yet.

That number is the minimum flowrate you need assuming a perfectly efficient system. Few systems are perfectly efficient. Chances are you still have to adjust for other aspects of your grow environment:

• For HID grow lights, add 50% for non-cooled lights and 20% for cooled lights
• For inline carbon filters, add 60%
• For silencers, add 20%.
• For CO2 enrichment, add 5%
• For hot, drier climates (think California), add 25%
• For hot, humid climates (think Florida), add 40%

Let’s start with our hypothetic 5′ x 5′ x 6′ tent that requires a minimum of 50 CFM and adjust for the following factors:

• You’re definitely using HID lights because they’re the best for the flowering phase (that means higher yields). Add 50% and now we’re at 75 CFM.
• You’re definitely using an inline carbon filter to minimize odor (discretion is important, after all). Add 60% and now we’re at 120 CFM.
• Oh, and don’t forget the silencer (ahem, discretion). Add 20% and now we’re at 144 CFM.
• CO2 enrichment? Yes, please. Add 5% and now we’re at 151 CFM.
• You live in Southern California because you love the mild winters. Add 25% and now we’re at 189 CFM.

Factor in some buffer for the length of your ductwork and any bends or elbows, and you can see how many inefficiencies the typical grow room has.

And I’ll say it again because it’s important: That number is a minimum. You can (and should) aim higher because you don’t want to run your fan on max output at all times. That’s a great way to burn out your duct fan, so look for a model with a fan speed controller.

How to Install an Inline Duct Fan in Your Grow Room or Grow Tent

It’s easy to install an inline fan in your grow room or grow tent.

1. Set up your grow room or grow tent.
2. Feed the ductwork through the desired ventilation port.
3. Mount any brackets or other hardware on the fan.
4. Attach the fan to your grow room or grow tent frame, either with any provided hardware of zip ties. Make sure you position the fan’s intake facing the open and not the side or corner of the tent.
5. Use a duct clamp to secure the fan’s exhaust to the ductwork and tighten.
6. If you’re using an inline carbon filter, use another duct clamp to secure the ductwork outside the grow room or grow tent to the filter.

This video shows how easy to install an inline exhaust fan really is.

How to Install an Inline Duct Fan in Your Grow Room or Grow Tent

It’s easy to install an inline fan in your grow room or grow tent.

1. Set up your grow room or grow tent.
2. Feed the ductwork through the desired ventilation port.
3. Mount any brackets or other hardware on the fan.
4. Attach the fan to your grow room or grow tent frame, either with any provided hardware of zip ties. Make sure you position the fan’s intake facing the open and not the side or corner of the tent.
5. Use a duct clamp to secure the fan’s exhaust to the ductwork and tighten.
6. If you’re using an inline carbon filter, use another duct clamp to secure the ductwork outside the grow room or grow tent to the filter.

This video shows how easy to install an inline exhaust fan really is.

6 Inline Fan Features That Matter

Many features that companies advertise on their products are just gimmicks to get you to add their items to your shopping cart. These are the features you should look for.

1. CFM (Airflow)

Airflow is the most important duct fan feature. CFM is how you measure a fan’s ability to ventilate grow rooms, HVAC exhaust systems, AV closets, or just cycle fresh air consistently during COVID 19.

You may also see one inline fan for grow rooms with a drastically different CFM than another despite the same diameter. Motor power, stator blade and rotor blade construction, and mixed flow design all impact whether two 4-inch inline duct fans have the same CFM.

But here’s the problem: You can’t always trust the CFM rating a company slaps on their product listing. Sometimes it’s measured under ideal conditions you’ll never experience in the real world, and sometimes it’s a flat-out lie. That’s why I recommend brands like TerraBloom and AC Infinity, who I trust to provide accurate CFM measurements.

The discount VIVOSUN fan listed above as an alternative? It costs less than both TerraBloom and AC Infinity’s comparable 6-inch fans but advertises a higher 390 CFM. You know what they say about something that’s too good to be true.

2. Price

Price matters, and that’s why I recommend TerraBloom. Some of AC Infinity’s products have fancier features, but they have a price tag to match. TerraBloom has every feature you need with reliable performance, a great price, and the personal experience that comes from dealing with a small business that cares about its reputation.

3. Variable Speed Control

Almost all inline fans come with a variable speed controller. Turning your fan up to 100% and letting it cycle the air in your grow room may be tempting, but it isn’t the best idea.

1. You don’t want to rack up higher electrical bills.
2. You don’t want to burn your fan out.
3. Airflow isn’t the only variable you want to monitor.

Humidity and temperature are important too, so a fan speed controller is key to maintaining optimal environmental ranges inside grow rooms. Some inline fans come with a sensor probe, thermometer, or other environmental monitor connected to a variable fan speed controller to make real-time changes to fan speed and air intake, which ensures optimal growing conditions.

A fan with a sensor probe will cost more than one without, but it can be a handy feature if you want a more hands-off experience. Otherwise, you can just use a thermometer or hygrometer (to measure humidity) and manually adjust intake as needed.

4. Construction

One reason VIVOSUN is able to slash their price is that their products aren’t made with high-quality materials. TerraBloom’s inline fan is encased in a durable brushed steel housing. VIVOSUN’s housing is made of plastic.

5. Quiet Operation

Another place where you get what you pay for. High-quality inline fans made from high-quality materials are built with—you guessed it—higher quality. You may not see that quality, but you can hear it. Better ball bearings, permanently lubricated composite fan blades, a stronger center hub, a thicker power cord, more efficient flow design, better insulation class weight—and those are just a few of the under-the-hood items that mean better intake and fewer air delivery problems for a wide range of applications.

Those features also mean quieter operation.

6. Power Cord Length

Make sure the fan you order can reach your outlets, and make sure it’s compatible with those outlets. Most fans are 110-120V and work with a standard household plug.

How to Make an Inline Fan Quieter

Quiet operation is a key feature for most home growers. If you’re growing cannabis plants, discretion is very important. If you’re growing other crops, you probably don’t want to deal with the constant buzz droning in the background.

The easiest way to enjoy quiet operation is to buy an inline duct fan that’s quiet to begin with. TerraBloom’s inline fans are ultra-quiet, as shown in the video below which demonstrates their 8-inch inline duct fan running at just 74.8 dB at max power. That’s the same noise level as a vacuum cleaner, which is pretty quiet for a fan moving 710 cubic feet of air every minute.

6 Reasons Inline Fans Are VITAL To Your Setup

Without adequate ventilation, your growing operation is doomed to fail before you even begin. Because of the cramped and isolated environment of a grow tent or room, you need to plan ahead to achieve a successful yield come harvesting.

There are 6 major benefits of using inline fans for grow rooms and grow tents.

1. Larger and faster yields 

With the right environment and constant ventilation, your plants will grow faster and offer greater yields.

2. Temperature and humidity control

Grow lights, especially non-LED options, run hot and heat up your environment quickly. Inline fans vent out hot air and replace it with fresh, cool air. A good fan also prevents hot or humid air patches for constant, even growth. Some fans, like the AC Infinity Cloudline T6, offer a model that comes with a variable speed controller that monitors the temperature and humidity in your grow room and adjusts fan speed appropriately.

3. Mold prevention

Mold thrives in humid environments with stagnant air. The constant movement of air and lower humidity levels in grow tents and grow rooms drastically reduces the risk of mold and other diseases or pests.

4. Keep plants breathing 

You couldn’t survive locked in a small box without an adequate air ventilation system. Neither can your plants, so an efficient fan like the TerraBloom EC fan or AC Infinity Cloudline T6 is a worthwhile investment.

5. Prevent odor

A grow room fan keeps any lingering odor away, which is important if you have plants with a strong smell (like cannabis). It goes a long way toward keeping things under wraps.

6. Inexpensive for great returns on investment

Inline fans come in a range of price points and are easier to fix as opposed to drilling a hole or ducting. They’re also one of the easiest ways to keep your grow environment hospitable for excellent yields.

What Are the Best Inline Fans?

I can’t give you a single model number for the best inline duct ventilation fan because needs vary by grow room, grow tent, or other grow space.

However, I can give you the manufacturers and product lines I trust.

TerraBloom EC Inline Fan Series

TerraBloom is an up-and-coming manufacturer whose fans sit in the sweet spot between features and price. They have all of the true need-to-have features like a variable speed controller and quiet EC fan motor with amazing build quality as seen with their durable, brushed steel exterior housing. TerraBloom also backs their fans with a 2-year warranty.

AC Infinity Cloudline T-Series

AC Infinity is the most recognized name for grow room ventilation. AC Infinity Cloudline fans (T4, T6, T8, S10) are some of the highest-selling inline duct fans, and the AC Infinity Cloudline T6 might be the most popular fan overall. They come with almost every feature you could want—and some you don’t really need—with a price tag to match. Many come with an automatic speed controller that monitors the temperature and humidity and adjusts the fan’s speed in real-time. Like TerraBloom, AC Infinity offers a 2-year warranty.

Vortex S-Line

Vortex models, like the S-Line S-600 fan, come with an incredible 10-year warranty. Compared to TerraBloom’s EC fans and AC Infinity Cloudline fans, the same diameter fan from Vortex has the same CFM as TerraBloom (a touch less than AC Infinity), with a speed controller, low noise level, more power draw, and top-of-the-line build quality in the most expensive package. Vortex S-Line fans are great for serious, indoor growers who put their grow room ventilation equipment to the test but are more than most beginner and intermediate growers need.