What Is A Carbon Filter and How Does It Work for Grow Room?

Grow tents require strong ventilation. And growers have multiple ways to make sure that happens.

But there are smells and odors inside grow tent, which you don’t want to come out and keep your house smelling like an intense hotbox.

For odour management in such scenarios, carbon filters are on rescue.

In this 2000+ words article, we’ll be taking you through a carbon filter 101 guide. We’ll learn the definition, the types, how they work, the cfm calculation, installation/setup guide and so on.

Grab a cup of coffee, and let’s master on grow room carbon filters-

What Is A Carbon Filter?

Carbon filter is a part of air exhaust system in an isolated space(grow tent, grow room, greenhouse etc.) They contain beds of activated carbon(charcoal) with tons of pores inside.

what is a carbon filter- carbon filter structure
Photo Source: Amazon.com

When air of a grow room or greenhouse is vented through a carbon filter, it traps the smell, dust, spores, pollen and other airborne containments.

As a result, your grow space stays free of bad smell, harmful chemicals, and unhealthy containments.

What is a Carbon Filter for in Grow Room?

Before digging deep, let’s learn about the purposes of carbon filter in grow room

Odor Management

For a grower, one of the hardest tasks is to keep the bad smell away. Specially, when you don’t want your neighbors to know about this ‘hobby’ of yours. 🙂

Fortunately, a carbon filter is able to trap all the smelly particles from the air, if air invented across the filter in a proper way. To make that happen, you’ve to deploy exhaust fan(s) to draw air and take that air through the filter before releasing outside.

Taking Impurities Out

Apart from right temperatiure, humidity and nutrients, grow plants need clean, fresh air as well. Impurities like air-borne pathogens can cause diseases in plants and ruin the whole grow yield.

And activated carbon has it’s the ability to scrub such impurities out of the air.  

To let your plants breathe freely, you’ve to set up a ventilation system where all of the air is taken through the carbon filter on regular basis.

To Cut Your Bills

There are many systems for air filtration. And some of them might cost you a fortune. But grow room air carbon filters are the least pricey one of them that costs not too much and still works just fine.

As growing indoor is a power-hungry business, a good carbon filter can keep the electricity bill down.

Quick and Easy to Setup

Another good fact about carbon filters is- they’re pretty easy to install. If you think about a carbon filter-fan combo, it can be put on the right place within minutes. All you have to do is set it up at the right height, and attach with ducting with clamps.

Types of Carbon Filter for Grow Room

Air filtration in grow tents can be done in many manners. Based on grow tent sizes, number of plants, ventilation system and budget, the choice of grow tent filters is made.  

For grow rooms, we can divide such air filters according to a few viewpoints- Filtration medium, fan-filter combo and diameter of filters.

Let’s learn about each of them-

Based on Filtering Medium

Carbon Air Filter

Most convenient and most efficient grow room air filters are made of carbon beds. Activated carbon filter beds, to be exact.

For creating the filters inside, charcoals are chemically and thermally treated and turned into activated carbon.

One of the properties of activated carbon is- they contain millions of pores. Resultantly, the surface area extends to 2000-4000 m2 in each gram of activated carbon to draw dust and smelly particles onto it.

In almost 100% of growing systems require activated carbon air filters anyways.

Our Pick: Amagabeli 6 inch Carbon Filter

Non-carbon Air Filter

There are a few other filters where non-carbon elements like particulate cabin air filters are used instead. Although carbon filters are pricier than this, particulate cabin filters are not as efficient as them.

As an example- particulate cabin air filters are able to remove the dust containment only. But activated carbon filters takes everything that particulate filters do as well as the odor and exhaust fumes.

If you’re is short of enough space to house a carbon filter, you may try putting the carbon filter outside of it.

Based on Filter-Fan Combination

Carbon Filters Only

These are more like solo carbon filters that you would like to have as replacements of your current one.

While getting such solo filters for your setup, keep in mind to match the CFM rating, the sizes, the flanges and the dimensions(both length and diameter).

However, make sure to pick up a model with a pre-filter provided with it.

Our Pick: VIVOSUN 4 Inch Air Carbon Filter

Carbon Filter-fan Combo

For most growers, a filter-fan combo is the best choices. The adjustment and installation take a minimal effort, as the fan and the filter are made to be equipped with one another.

With many models, there are also speed controller devices and rope hangers with the fan-filter duo. You can call such packages the 360-degree ventilation solution for any grow system.

Our Pick(with speed controller): VIVOSUN 6 Inch 440 CFM Inline Fan with Speed Controller

Our Pick(without speed controller): VIVOSUN 6 Inch Air Carbon Filter

Based on Diameter

4” Carbon Filters

4 inches carbon filters are with the smallest opening size. They come with CFM ratings around 150-250 CFM. And such filters are ideal for 4×4, 4×7 or 4×8 tents, where you can grow 4-6 plants(ScrOG style).

Our Pick: iPower 4 Inch Air Carbon Filter

6” Carbon Filters

Carbon filters with 6” sized diameters are able to extract air around 400CFM rate. When you want to equip only one carbon filet in your 8×8 or 10×8 grow room, this is the one that you might go for.

Our Pick: Phresh Filter 701005 Filter

8” Carbon Filters

8 inches filters are more suitable for grow rooms rather than small or medium-sized grow tents. As they come with a CFM rating around 600-700 CFM, they can be quite sufficient for grow rooms of 12×12 size.

Our Pick: VIVOSUN 6 Inch Air Carbon Filter

10” Carbon Filters

10” carbon filters are the elder versions of 8” models. Providing an air extraction rate of 1100-1200 CFM, growers are more likely to stick to these models.

Our Pick: Phresh Filter 10 in x 24 in 850 CFM Carbon Filter

12” Carbon Filters

This is the largest kind of carbon filters of them all. Usually, when you need ultra-efficient air extraction at a rate of 1400+ CFM, these are the ones you should go for.

Our Pick: Phresh Filter 12 in x 24 in 950 CFM Filter

How Does A Carbon Filter Work in A Grow Room

Carbon filters are super strong combaters when it comes to fighting allergens, pathogens, harsh pollutants and odors.

But how the heck they work?

Well, as the name suggests, there are layers of activated carbon beds(charcoals) in each carbon filter. The carbon particles provide a surface area full of pores. Each gram of activated carbon has 3000 m2 of such surface.

Now the question is, what is activated carbon?

Activated carbons as just regular charcoals, but taken through a process it’s gas trapping capacity.

This process is done majorly by injecting hot air or steam into the charcoal. That creates a lattice of pores in the carbon. As a result, the surface area is vastly increased.

As you’ve read a while back, a single gram of activated carbon can have hundreds of square meters of internal surface area.  

Porous Charcoal
Photo Source: Squarespace.com

Nature of this surface full of pores is to attract pollutants and allergens from the nearby air. The process is called ‘Adsorption’(not Absorption). Through this process, the carbon bed gets to absorb various organic chemicals(gas, dust).  

As an end result, pollutant particles and odor creating gas molecules are trapped onto the surface of activated carbon(charcoal) bed. And what you get is a pollutant-free, odor-free grow tent.

Carbon Filter Cfm Calculator for Different Grow Tent Size

At this point in the discussion, we’ll learn how to calculate the right size(capacity) of carbon filter for your grow tent. And we want you to be super-attentive to the calculations we’re about to do-

Step 1: Determine Your Grow Tent Air Volume

First of all, determine the total volume of the grow tent. This will let you know how much air is there inside the tent/room at any given moment.

The formula is simple-

Volume of grow tent= Length x Width x Height

Example: 10ft x 10 ft x 8 ft= 800 Cubic Feet

Step 2: Decide How Much Air to Extract In Every Minute(CFM)

Now, you’ve to decide how many times you want to renew the entire air every hour. For small tents, it can be 40- 60 times in an hour(once in every 1.5- 1 minute). For larger grow tents like 10×10, 8×8, 4×8, we prefer it to be 30-20 times in an hour(once in every 2-3 minutes).

Let’s say that we want to empty up our 10×10 grow tent air once every 3 minutes. So, air volume to extract in each minute(CFM)-

Air volume to extract(for fan) in 1 minute= 800 cubic ft./3= 266 CFM

So, the fan should be able to take the air out at 266 CFM rate.

Step 3: Calculte The Carbon Filter CFM

Now, it’s time to determine the capacity of the carbon filter and the fan.

In this regard, let us inform you that, using carbon filter on an extractor fan resists the fan’s efficiency. To be exact, using a carbon filter decreases the fan’s efficiency by about 25%.

So, you need to equip a carbon filter with 25% more CFM rating in order to let the fan extract the required amount of air in each minute.

So, the CFM rating of the carbon filter would be-

CFM Rating of Carbon Filter= 266 CFM x 1.25= 332.5 CFM

Things to remember-

  1. The air extraction frequency may vary based on the size of the tent, and the types of plants.
  2. The resistance of carbon filter on the performance of the fan may vary based on size, diameter and connector type.
  3. The resistance on the performance of fan may also depend on the length and material of ducting. As an example, straight hard cast ducting of 25ft may lose 3% of CFM efficiency of the fan.
  4. The resistance on the performance of fan may also depend on the ducting angle. As an example, a 90-degree bend may loss 1%-4% of the overall efficiency.  

However, here’s a pre-formulated carbon filter size calculator. Hope you’d have a few minutes to look that up.

Also, this video on carbon filter size can be a good help-

Where and How to Use Carbon Filter in Grow Room?

Most growers prefer installing the carbon filters inside the tent, where it can be combined with the ducting and the inline fans. However, if you’ve short space to house a full-size air filter, carbon filter placement can be outside as well.

However, considering that you’re setting it up inside, here are the quick steps of installing a carbon filter-

Step 1: Take out the filter from the package, put the pre-filter(if any) on it.

Step 2: Place the filter on the exhaust along with rope ratchets. Make sure to put the exhaust ducting, filter and the exhaust fan in one line.

Step 3: Secure the connections by duct clamps. Make sure the connection is air-tight.

Step 4: Power the fan up and check for any leakage throughout the whole way.

On a side note, if you want to create your own carbon filter at home, here is the guide.

Carbon Filter Maintenance 101

Carbon filters are mechanical setups to play an important role in odor/impurities management. To keep them in their pick condition, keep these maintenance tips in mind-

Clean the Filter

Cleaning carbon filters is one must-to-do task to make the best use of it.

Firstly, remove it from grow room, and take that into an open space. Shake it vigorously to remove any trapped dirt or dust inside.

Now, spray water on the carbon beds and submerge it into the water. Don’t forget to mix the water with a mild soap before putting the carbon filter in it.

Keep it under water for 15 minutes, and take it out. Now, dry it under heat or sunlight.

Read our complete cleaning guide for more in-depth instructions.

Vacuum and Dry Up

If you don’t want to deal with the mess of cleaning it off every month, a vacuum cleaner can be an alternative.

In every alternative week, vacuum-clean the activated carbon beds to remove excess carbon and dust particles. Before vacuum cleaning, don’t forget to take the carbon bed out.

Don’t Use It Beyond It’s Lifetime

If you’re serious about the odor management, you shouldn’t expect a carbon filter to do that forever. Like every other device, it has a certain lifespan. And it’s best to change that right after that time.

Usual carbon filters are likely to function properly for 1-1.5 years.

However, you should have an eye on the durability of a carbon filter while you’re buying it.

Can You Grow Without Carbon Filter?

We’ve seen many first time growers ask themselves- do I need a carbon filter in my grow room?

Well, the question itself replies you back with another question-

“Do you mind if the smell inside the grow tent comes out and spreads around?”

If the answer is no, then there is no other way than using a good quality carbon filter in your grow system.

However, if you’re growing outdoor where you can extract the air without filtering the odors and leave them at the environment, then you might not need a carbon filter.

As you know, that doesn’t even make a sense anyways.


I'm Saleh, a hobbyist DIYer, and a blogger. Whatforme.com is my little place on the web to express what I've learned first-hand, specially about home improvement.

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