The growroom: Carbon filters

Once your plants start their flower period, they will start to smell, Heavily! The more buds, terpenes and trichomes, the harder it smells. This cannabis smell is very distinctive and even people not familiar with cannabis will recognize it. In areas where growing is illegal, this might cause problems as neighbours or “the law” sense a smell of your plants. Thats why you need to get yourself a good working Carbon Filter! 

In this article:

What is a carbon filter

Carbon filtering is a specific method of filtering air or water. This type of filter uses activated carbon to take out contaminants and impurities using chemical absorption (which is very effective). These filters come in many different forms and sizes but for growing cannabis there is just 1 type we need:

The carbon filter we use for cannabis is being used to get the smell out of the air that is leaving the growroom. They always look like some sort of roll and the size varies based on the size of the growroom/ how much air is going through. This “roll” sucks up the air through it’s carbon casing using a strong extraction fan thats is mounted on the filter. This extraction fan blows the air outside the growroom using the tube that is attached to the filter.

This method of filtering works extremely good for the intense smell of cannabis. The air that eventually goes out will be free of smell.

How does a carbon filter work?

Carbon filters are very effective when it comes to reducing the smell in the air. Thats why they already being used for years in the cannabis cultivation. The thing that makes these filters so effective is the activated carbon in them. Activated carbon has some unique properties that makes it the perfect element to filter the air from smell!

This “activated carbon” has been treated and crumbled down to create the biggest surface of carbon thats possible. This will improve the absorbtion of contaminants massively!

The activated carbon that you can find in these filters comes in powder form most of the times. Next to that it is treated to be extremely porous. This is to create a bigger surface of carbon so it is able to absorb more contaminants then “normal” carbon.

This activated carbon is able to absorb/remove contaminants by something we call “chemical absorption”. Each small piece of treated carbon offers a huge surface and a lot of pores. These pores will “trap” the contaminents out of the air leaving you with clean, odorless air.


Eventually, a carbon filter gets “full” after a certain time of filtering. This means thats the pores in the activated carbon is filled with contaminants and can not absorb any more. This makes the filter useless. Always keep checking your filter and replace the carbon on time! 

What size carbon filter do I need?

The size of your carbon filter + Strength of the extraction fan is something you need to take a good look at before building your growroom. The filter has to be big enough to manage all the air that needs to get out and the fan needs to be strong enough to produce a strong air-circulation in your growroom. This depends mostly on 2 things:

  • The size of your growroom/amount of air that needs to be filtered
  • The amount of heat your light(s) emit

Cannabis plants do need fresh air to stay alive and perform photosynthesis, thats why it’s important to have a strong flow of fresh air coming in, and “old” air going out. So based on how much air is in your growroom, you need a fan thats able to blow/suck everything out in +- 60 seconds. The filter plays a role in this: The bigger the filter, the easier it is to suck air through it (so the quicker you replace all air in your growroom).

It also makes you able to control temperatures and humidity levels. As one of these rises (Due hot lights or watering of your plants), you could turn up the extraction fan in order the get more fresh, cold and dry air in the room. This will lower the temperature/humidity and creates a more suitable environment for your plants.

When buying a “grow-tent set””, you will recevie a carbon filter + extraction fan that is perfect for that particulair tent. Pretty easy! However when creating your own room or tent, you need to find out the size and strength of your filter + Extraction fan. The next video will help you with this: