What Size Carbon Filter Do I Need?

Here we’ll show you exactly how to calculate what carbon filter you need for your personalized grow op.

Calculating the Size of Your Carbon Filter

The size of your carbon filter depends on how many times an hour you will be flushing the air and the total volume of the area you’re growing in. Certain cannabis growers target 30 times an hour, while to remove all traces of your plants’ smell go 60 times an hour. Calculate the cubic volume of your grow tent, room, or area using this formula:

(Length X Width) x Height = Total Volume in Cubic Feet

Now that you have your total volume, divide that value by 5 to get the Total CFM needed to flush the air every 5 minutes. Let’s see how that works out with a practical example.

If your grow tent measures 4 × 4 × 4 feet would work out as follows:

(4 feet x 4 feet) x 4 feet = Total CFM or

16 feet x 4 feet = 64 CFM

64 CFM/5 = 12.8 CFM carbon filter needed

As you can see, when you’re using a grow tent, almost any carbon filter will be capable of clearing all odors quick enough.

Keep in mind that ideally you need a carbon filter which is a match to the CFM rating of the exhaust fan. There is nothing wrong with buying a larger filter than you need. Carbon filters last long, giving you more than enough room to upgrade to its capacity at a later stage when your grow op is larger.

Negative Air Pressure

A carbon filter simply placed within the passage of your air circulation will have a limited effect, but to truly capitalize on your ventilation and filtration, you need a sealed system with negative air pressure.

Odors have no choice but to be sucked into the flow of your ventilation system and pulled through the carbon filter in the process. Negative air pressure is the only way to guarantee that your carbon filter is working as you want it to.

Where Do I Need a Carbon Filter?

Carbon filters are commonly first fitted on your intake inlet but to contain smells two filters are needed. The fresh air blown into circulation needs to be free from toxins, with most intake fans coming with a carbon filter and protective pre-filter as standard.

If you still experience a level of odor in the vicinity, then the saturation is too high, and you’ll need a carbon filter on the exhaust line as well. Most growers fit one as a standard part of their negative pressure setup as this guarantees that all smells are locked in as long as the filters match the CFM of your fans.

Large Grow Operations and Removing Carbon Filters

Certain greenhouse configurations will reach an acceptable level of odor in the air. Growers will then take a carbon filter off the exhaust line at one or more of the outlets of their system. The removal of carbon filters before saturation is reached is employed due to how much better filters work when set at the perfect performance standard.

The slower air flows through a carbon filter, the closer to optimal the carbon filter performs adsorption. Fan speed controllers are used to slow the flow rate and thus drop the concentration of smells in the air to the desired level. Most growers will never reach this scale but if you own a greenhouse it is worth keeping in mind.

Filter Any Room, Box or Grow Tent

With the right configuration of extractor fans with enough CFM to drive air circulation in the room, carbon filters can even be used to contain the smell of marijuana being smoked, vaped, or even baked.

No matter how pungent the smell may be, set an inline fan and carbon filter in place, and a powerful exhaust sealed and set up, and the negative air pressure takes care of everything. You’ll still need to find quiet inline fans or build a dampening box to conceal them, but the smells are taken care of.