What Size Intake Fan for Grow Room or Tent Do I Need?

Wondering what size intake fan for the grow room or tent you need? The intake fan is crucial for bringing in fresh air while the exhaust fan removes hot, stale air. You need both to create an optimized client conducive to explosive plant growth. But, so many growers - hobbyists and commercial cultivars alike - get their intake fan sizing wrong. So today, we'll provide a detailed guide on how to size your intake fan properly.

If you size your intake fan too large, you won't be able to create that negative pressure in the space that leads to an optimized ventilation system. You'll also be wasting money on an oversized fan that racks up an expensive energy bill. But, if your intake fan is sized too small, it won't bring in enough fresh air and CO2 - and your plants will suffer as a result.

Fortunately, your question - what size intake fan for grow tent or grow room do I need? - will be answered in the following paragraphs. By the end of our discussion today, you'll feel confident in sizing your fan to perfection and creating an ideal climate for your crop.

Let's start by explaining the role your intake fan plays in creating a balanced, fine-tuned environment.

What is the Intake Fans Purpose in the First Place?

The intake fan's primary purpose is to bring in fresh air into the growing space from the outside. This air will then be circulated by an oscillating fan and vented out by your exhaust fan to create negative pressure. The ideal situation is to have your intake fan slightly less powerful than your exhaust fan so that you can maintain that negative pressure where plants can thrive. But to truly understand the significance of your intake fan, let's go back a step further - and talk about the indoor growing climate itself.

When growing plants outside, your crop has access to all the fresh air - and most importantly, CO2 - necessary to reach its full genetic potential. However, when growing plants indoors, your goal is to create a synthetic growing environment - that means bringing in grow lights, ventilation equipment, and other supplies. Besides lighting, the ventilation system is the most important element of a successful indoor growing setup. And there are a few key elements of this system: the exhaust fan, the circulation fan, and the intake fan. Each plays a key role in dialing in your grow room or grow tent climate.

Many growers try to get by without an intake fan - allowing the exhaust fan to pull in air through an open duct passively. This typically doesn't bring in enough CO2 - and plants become "CO2 starved". As a result, they're unable to reach their full genetic potential - despite using the best fertilizer, most powerful LED grow lights, and the best seed genetics.

So, you need an intake fan. But why can't you just use the same size fan as your exhaust fan? Why does proper intake fan sizing matter so much? Keep reading to find out...

Why Proper Intake Fan Sizing is Paramount

While an exhaust fan is important for removing hot, humid air - the intake fan is what actually brings in fresh CO2-rich air from outside. This makes it one of the most important components of your grow room or grow tent ventilation system!

There are a few key reasons why proper sizing matters:

  • If your intake fan is too small, it won't bring in enough fresh air to meet the needs of your plants. This can lead to "CO2-limited" growth where your plants don't reach their full potential.
  • If you size your intake fan too large, you won't be able to create negative pressure in the space. Instead, atmospheric pressure will push stale air into the space through any tiny openings - this is called the "chimney effect".
  • An oversized intake fan will also rack up an expensive energy bill needlessly.

As you can see, it's important to size your intake fan properly so that you can create a balanced, healthy growing environment for your plants. But unfortunately, what size intake fan for grow room isn't a one-size-fits-all topic. Let's take a look at some of the key factors affecting ideal sizing.

What Affects the Ideal Size of Your Intake Fan?

There are a few key factors that affect the ideal size of your intake fan:

  • The size of your grow room or grow tent - this is probably the most important factor! A larger space will require a more powerful fan to achieve proper airflow.
  • The number of exhaust fans in the space - the more exhaust fans you have, the more fresh air will need to be brought in to maintain negative pressure. You need to ensure a good balance of the size of your exhaust fan compared to your intake fan. More on that in the next section.
  • The type of plants you're growing - some plants (like cannabis) are "CO2 hungry" and require large amounts of CO2 to reach their full potential. These types of plants will require a larger intake fan.

So, What Size Intake Fan for Grow Room or Tent Do I Need?

Ready to discover what size intake fan for grow tent or grow room is right for you?

There are a few ways you can go about sizing your ventilation system as a whole. Our guide on the CFM meaning is a great starting point - as you'll need to understand how to take the dimensions of your growing space and turn that into a CFM recommendation. You can take a look for the full breakdown, or, keep reading for a quick summary of how to calculate CFM:

The first step is to calculate the volume of your grow room or grow tent in cubic feet: length x width x height. Once you know the volume, it's time to decide on the number of air changes per hour (ACH) you want. ACH is a measure of how many times the entire volume of air in your space will be replaced each hour.

For example, if you have a grow room that's 1000 ft³ and you want an ACH of four, you'll need a fan that can move 4000 ft³/hr.

But - let's say you've already got an exhaust fan in your system, and it's sized properly. From there, figuring out what size intake fan you need in your grow room or grow tent is easy. As we mentioned earlier, you can typically size down about 20-30% on your intake fan. If you go with TerraBloom commercial inline duct fans, setting up an optimized ventilation system is even easier. You can buy two of the exact same fan - and power down one of the fans by 30-40% of the flow of your exhaust fan for a perfect setup. Or, simply size down on your intake fan a bit - if you have an 8" exhaust fan, a 6" intake fan will be ideal.

Can I Not Just Use One Single Fan for Intake & Exhaust?

A common question we get here at TerraBloom is whether or not our fans are reversible. Can't you just reverse the flow for intake and exhaust - like how you'd reverse a ceiling fan? The answer is no - because our fan's design has been optimized for quiet, efficient performance. This requires the use of a 3-dimensional cone-shaped blade - rather than the flat blades you may be used to with window or box fans.

This design creates the perfect intake fan - but only for pushing air in one direction. Even if the motor would spin in the opposite direction, it would be pointless. Why? Because the ventilation system is lacking the negative pressure we've mentioned throughout this discussion. And, air flow would be lacking as a whole.

With that said, invest in separate intake and exhaust fans if you are looking to create a fine-tuned ventilation system. Trust us - your life will be easier, and your plants will thank you come harvest day!

What Size Intake Fan for Grow Tent or Room Do I Need? Wrapping Things Up

We hope this article helped clear up any questions you had about what size intake fan for grow tent or room is best for your setup.

In summary, your intake fan should be about 20-30% less powerful than your main exhaust fan. To accomplish this, you can buy two adjustable inline fans and dial back the power on the intake unit by 30-40%. Or, you can buy two inline fans of varying sizes - for example, an 8" fan as your intake and a 10" fan as your exhaust. Either of these scenarios will create negative pressure in your growing space so your plants can thrive.

At TerraBloom, we have a full lineup of inline duct fans to help you optimize your ventilation system - from 4 inch inline duct fans, 6 inch inline duct fans, 8 inch inline duct fans, 10 inch inline duct fans, and even 12 inch inline duct fans. Just add one of our air carbon filters and an adjustable fan speed controller - and you have reliable, efficient air movement that will keep temperature and humidity at proper levels - while bringing in fresh CO2 on autopilot.

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