So what is a scent, anyway?
Let’s start with the basics: what is a scent? A scent is what we smell when we inhale a certain concentration of “odorant molecules” that react with receptor cells in our noses. These molecules are only found in volatile organisms, which are organisms that can easily be turned in to gas. That’s why things that break down easily give off scents, versus materials like steel, rocks, and minerals that do not have a scent.
Photo: Purdue University
Scents vary in intensity depending on the type of odorant molecules the source gives off, and the conditions around the scent’s source. The smell of trash, for example, intensifies with increased heat so the hotter it gets the more intense the smell of trash becomes. Chemicals that dissolve in water (like dish soap) have inherently strong scent molecules which are meant to release strong scents once they’re broken down. There are tens of thousands of scents in the world, but the human nose can only detect around 10000 of them. Why does all this matter? Because even though you can’t smell the scent of your growing plants and their medium, pests and insects sure can Not only is odor control good for discretion, but it’s also a measure in pest control. Know what your plants should smell like is a great way of understanding what your plants need. If your growing plants should have a certain smell at a point in its life and it doesn’t, chances are the plant’s suffering from some sort of deficiency.
Handling Strong Scents with Duct Fans & Carbon Filters
You know ‘em, you love ‘em: Carbon Filters. They’re pretty much everything you need to help neutralize the odors in your grow room all in one unit. Filters have activated carbon in them that helps clean the air that’s pushed into it, leaving you with fresh air that doesn’t contain all of those odor molecules. When the funky air passes through the filter the carbon will absorb those smells, and the air that’s released will be free from smells. But to make them work you have to make sure you have the right size and the right setup for air to come into the filter and exit it neutralized.Sizing Your Area for the Right Fan & Filter
The most common (and highly recommended) size for any indoor grow is 6” fan and filter combination, but you’ll also want to be sure you have the correct size for your growing space. Filters will have a certain CFM (cubic feet per minute) they can handle, so you’ll want to make sure you calculate the volume of your growing area to make sure your filter can handle the odors you’re trying to eliminate. How to Calculate CFM Exhaust fans and filters are usually rated by CFM, or “cubic feet per minute”. The CFM rating is a reflection of the rate that the fan can replace stale air with fresh air or its “fresh air exchange”. The first thing you do to figure out the CFM you need is to take the volume (LxWxH) of your grow room. Most growers want their grow room to exchange stale air with fresh air every 3 minutes, so take your volume and divide that number by 3. After that, you'll take into account light temperatures, the use of a filter, and the environmental conditions of your growing area. Add 25-40% to the total CFM of your grow room for warm and humid temperatures. HID’s should account for about 15% to take their heat into account, and 20% should be added if you plan on using carbon filters (Note: if you're using LED's you do not need to calculate 15% for lights) But no matter the size filter you have, we recommend replacing the filter rather than trying to clean them. Running your carbon and the metal filter through water will not do much to help the smells, and it’s likely to damage carbon, rendering it useless. So let's put this in the action... Let’s say we’re in a grow room that’s 10x10x12ft, which gives us a volume of 1200 cu.ft. Now take that number and divide it by 3 for air exchange and you’ve got 400 CFM as a base number for the necessary CFM needed for your growing area.- If your grow room gets up to around 97°F so it’s pretty warm- that means we’ll add 25% of 400 (100) to the base CFM.
- You’ll probably also use a filter, which is another 20% (80), and if you’re using a CMH light we’ll add 15% (60) to take light temp into account.
- From there you’ll take 400 + 100 + 80 + 60 and add them up, giving you a total of 640 CFM.
- That means your fans have to be able to move at least 640 CFM of air to give you the ventilation your plants need.