Grow Room Odor Control: The How and Why

Controlling Grow Room Odor Is Essential.

Grow Room Odor is one of the most common reasons indoor grows to get ripped off and/or raided by the police. Preventing others from being able to smell your garden is one of the most effective and affordable security measures you can use. The bottom line is if they can smell it, they know it’s there.

Growers, big and small, need grow room odour control.
Marijuana grow rooms aren’t designed to be sealed from all outside air. A successful marijuana grow room needs ample airflow (unless you have a sealed room with CO2 supplementation but those are very expensive to build). You need to intake fresh air and exhaust the hot, stale, stinky air outside to have healthy plants and a bountiful harvest.

How to eliminate Grow Room Odors

The most cost-efficient way to eliminate odour in an indoor grow environment is with a carbon filter aka carbon scrubber (you will see those words used interchangeably. They mean the same thing). A carbon filter is designed to filter organic odours, mould spores, dust particles, and other allergens from the air passing through it.

This will help get rid of the dank smell your plants are pumping out (no, it will not make your finished product any less smelly.) and also improve the overall environment that your plants are living in.

Do you want dirty air going into your lungs? Of course not, and neither does your plant. Plants don’t have lungs but they do have “stomata” which open and close to allow the intake of carbon dioxide (the good stuff for plants) and the release of oxygen (the bad stuff for plants). You can read more about stomata at Berkeley’s website (warning: it gets geeky in there, we like to keep it simple here).

How do Carbon Filters work?

A carbon filter is a container filled with activated carbon and one exhaust hole. Attach a fan and let it pull air through the outer mesh and the activated carbon contained inside. All the particles and odours become trapped and neutralized by the carbon allowing fresh and clean air to be expelled.

The simplest way to use a carbon filter is to place one on the floor inside the grow room. No ductwork is necessary. This will circulate the air within the grow room and cleanse it of smell.

Carbon Filter Sizes

When it comes to carbon filters there are three numbers you need to know.

1. The diameter of the hole the fan attaches to.
2. The overall length of the carbon filter.
3. The CFM (cubic feet per minute) rating of the filter.

You match the diameter of the filter to the diameter of the fan you are using. Standard grow room fans come in sizes ranging from 4 to 14 inches. More on how to select the proper sized fan in a minute.
You will determine the overall length based on how much physical space you have and depending on your CFM requirements.
The last number is the rated CFM (cubic feet per minute). This is how many cubic feet of air will be exchanged per minute. You want to match the carbon filters rated CFM with the rated CFM of the fan you want to use. More on calculating required CFM in a moment.

Pro tip: if you have a fan with a much lower CFM than your filter it will not remove the odour particles properly. It will also reduce the life span of the fan. If you have a fan with a much higher CFM than your filter it will cause air to flow through the carbon filter too fast and reduce the effectiveness.

Remember you want the CFM of the fan and the carbon filter to be as close as possible.

What size carbon filter do I need for my grow room?

The ideal carbon filter size will depend on how many carbon filters you have and the overall size of the grow room. In an ideal world, it is better to have two half-sized carbon filters on opposite ends of the room than one large carbon filter. Ideal comes at a price so for beginners I would recommend investing in one carbon filter and upgrading later if needed.

I recommend a fan/filter setup that is powerful enough to circulate the air once every two minutes. To get the correct sized fan/filter setup you need to find the total cubic feet of your grow area.

CALCULATING REQUIRED SIZE

Don’t worry, even if you didn’t pay attention in math class it’s REAL easy.

Take the width, the length, and the height of your space and multiply them together. (Volume of Room)

I know, its hard. Just stay with me here. If you have a 10′ x 10′ room with 8′ ceilings you do 10x10x8 and get 800 Cubic Feet.

To circulate the air once every two minutes you need a fan that is powerful enough to move 400CFM.

You also have to calculate the reduction in airflow due to the carbon filter. Fortunately for you, that is some math we won’t get into here. I use 20% as a rule of thumb. For our example, you’d want a fan and filter rated for around 500CFM.

Below is the chart on the size carbon filter you need based on your required CFM.

Centrifugal Fan Chart

Keeping with the example you would ideally go with the 6″ x 24″ carbon filter and simply find a fan that blows around 550 CFM and has a diameter of 6″. That was easy. (Learn more about CFM at Wikipedia.)

Setting up your carbon filter.

A carbon filter is one of the easiest things to set up in an indoor marijuana grow. Place the bottom of the carbon scrubber on the ground with a fan on top of the carbon scrubber sucking the air up and through the filter. Done! I recommend securing the carbon filter to the ground or keep it somewhere it won’t get knocked over.

To easily secure the filter to the fan a strip of foil tape will do the trick but it isn’t necessary.

You can also mount the filter on the wall or ceiling. Besides freeing up space there isn’t much benefit to mounting the carbon filter to the ceiling unless you are attaching it to your exhaust.

Remember carbon filter and fan setups can weigh upwards of 100 pounds (~50 kilos) so they need to be secured to the wall or ceiling properly.

Life expectancy of carbon filters.

The life expectancy of carbon filters varies. Some of the variables are how dirty your grow room is if it has a pre-filter or not, the grow room humidity, and the quality of carbon used in the filter. Cheap knockoff carbon filters aren’t worth it. Carbon filters generally last between 1 to 3 years before the carbon inside needs to be changed.

How do you know when to replace the carbon?

Pretty easy, once it stops removing the smell. If you can smell weed coming out of your exhaust it is time to replace the carbon.