Activated carbon is a form of carbon that has been processed to make it extremely porous (absorbent). Thus, activated carbon has a very large surface area available for absorption or to react with chemicals. Only one gram of activated carbon contains a surface area of approximately 500 m² (or about 2 tennis courts).
Carbon filters are most effective at removing volatile organic compounds (VOCs) from the air. VOC’s are organic chemical compounds that have high enough vapor pressures under normal conditions to significantly vaporize and enter the atmosphere. A wide range of carbon-based molecules, such as aldehydes, ketones, and other light hydrocarbons are VOCs. Simply put - for our purposes, they are molecules that have or are "smells".
So Carbon Filters are designed to remove smells, chemicals, dust, & fungal spores from the air.
In order to choose the correct filter and fan, the first step is to figure out what size filter and fan are appropriate for the volume of air being “cleaned.” (The Grow Room Volume)
Volume of a cube is found by multiplying the length by the width and multiplying that by the height of the room. A room that is 12 feet long, 8 feet wide, with 10 foot ceilings (12’x8’) x 10’ = 960 cubic feet of air.
There are two ways air can be cleaned using a carbon filter: exhausting or scrubbing.
Exhausting is when the air that has passed through the filter is vented out of the room, usually by means of ducting.
Scrubbing is when the air that has passed through the filter is returned into the grow space over and over again. When scrubbing, all of the air in the grow-room is cleaned so often that all of the air in the space seems filtered. This method will require a larger fan/filter combination in order to achieve the desired results.
Before moving on, it is important to mention that all CFM (cubic feet per minute) ratings are not equal. Many companies do in-house testing to determine the strength of their fans. A company can make a fan, test it “in-house”, and greatly exaggerate the strength of their fans because there is no oversight. (It would be like grading your own test…) The better companies use an independent third party laboratory to test and certify the strength and ratings of their fans. (Like a teacher grading your test.) CAN Filter Group uses the AMCA (the International Air Movement and Control Association.) The CFM ratings of CAN Fans are very accurate.
According to CAN Filter Group, when exhausting a grow kit, all the air needs to be cleaned within 3 minutes. Divide our 960 cubic feet by 3, this gives us 320 CFM and choose a fan that has a CFM of at least 320 CFM (always go bigger because fans lose power due to back pressure - the resistance of being hooked up to a filter or ducting.)
• A filter will reduce the air flow of a fan by between 15% and 30% (even a can fan MAX losses 15+ %)
• 25 feet of ducting without any bends will reduce airflow by 5-7%
• A 30º Bend in duct work can reduce air flow by 20%
• A 45º Bend in duct work can reduce air flow by 40%
• A 90º Bend in duct work can reduce air flow by 60%
• Also note that temperature & humidity will effect airflow
According to CAN Filter Group, when scrubbing, all the air needs to be cleaned within 2 minutes. Divide our 960 cubic feet by 2, this gives us 480 CFM (cubic feet per minute) and choose a fan that has a CFM of at least 480 CFM.
So if you know the size of the fan necessary you now need to match it to the appropriate filter. All CAN filters have a label that says the recommended CFM for exhausting or scrubbing as well as a minimum CFM for the filter to function properly. Usually the scrubbing CFM will be twice that of the exhaust CFM. You really need to match the fan to the filter for it to work properly.
There is a little note on the filter regarding a minimum of 0.1 seconds contact time…this refers to the amount of time the air passing over the carbon must remain in contact with it in order to be cleaned. If you place a 1000 CFM fan on a 200 CFM filter, the air passing through will be moving so quickly that the air will not have enough time in contact with the activated carbon to be “cleaned.”
CAN Filter Group has 3 models of Fans:
S – The smallest fan has a loss of 20-25% under load or pressure (when attached to ducting or a filter)
HO – are S models with “beefed up motors” and have a loss of 15-20% under load or pressure
MAX - their best fans have a loss of 5-10% under load or pressure and use less electricity than an HO model.
A few side notes:
It is always better for the fans to be set up where they are pulling air through a filter and not pushing. There are a few reasons for this. Pulling through the filter with the fan mounted on top allows you to utilize the pre-filter (the white polyester wrap on the outside of the filter) to remove dust and larger particles before they can enter the carbon filter and clog it. Also, the outside of the filter has more surface area than the inside of the filter. This means that the air will have less resistance and will flow through the filter with greater ease.
It is better to push air through the grow lights instead of pulling. This is a relatively new philosophy, but one which has its roots (no pun intended) in sound theory. The idea is that if there is a gap in ductwork, or a leak/unsealed point in a reflector, then the fan pulling through the lights would in-fact be drawing in air from the grow room, which may be “dirty” (for example - having an aroma of dead fish from organic fertilizer). To avoid this, if the fan is located at the beginning of the run of duct work and thus pushing through the lights then the worst case scenario would be a small loss in CFM as the air from the duct work escapes into the grow room…this is an acceptable loss in light of the possible risks…
Another reason to push through lights instead of pull is that fans are designed to function below a maximum temperature. A 1000 watt HPS light produces 3,400 BTU (British Thermal Units) of heat per hour and, as a result of that, the air being ducted out by the fans gets very HOT!
• Can fans have a maximum operating temperature of 187ºF
• S&P TD Series Inline Fan 150 & larger have a maximum operating temperature of 140ºF
• EcoPlus Classic Fans have a maximum operating temperature of 122ºF
* Although fans may continue to operate at temperatures above those mentioned doing so will shorten their life span, and void their warranties.
It is also better to run 1 larger fan pushing through a length of duct than to run 2 smaller fans with one pushing and 1 pulling for the above mentioned reasons.
When the air has high humidity (over 70%), the pores of the carbon can and do get “clogged” with water molecules and the filters become much less effective. They will return to proper working condition when the carbon dries back out.
We always get 2 questions from customers:
1. “Can I use only 1 fan and pull through my carbon filter & MY LIGHT TO EXHAUST BOTH MY LIGHT AND CARBON FILTER AT THE SAME TIME?” This sounds good because they only have to buy 1 fan, not 2, and it is all done in one easy step. BUT it will make both the air filtration and the air cooling of the light less effective. A fine carbon dust will be pulled from the filter and will coat the inside of the glass in the reflector as well as the bulb. If they are intent on doing this, then explain they will need to wipe down the inside of the reflector and the bulb at least once per week. Also, it will shorten the lifespan of their bulb(s).
2. “Can I just buy bulk carbon when my filter is done and re-pack it myself?”
The answer to this is NO! The filters are machine packed and not even with a sledge hammer are they going to fit the same amount of carbon back into the filter. The carbon can be added to a compost pile and will break down nicley. The housing can also be recycled, which is made of steel.
A filter is done when they stop working, so we let the customer’s nose be the guide. Generally filter life is between 9 and 18 months. A more exact way of knowing is to weigh the filter. When a filter gains 15% of the original weight of the carbon, it is generally finished (they gain weight as they fill with odor particles). When a customer gets home and they weigh their filter, let’s say a Can 100 weighs 100 lbs when new. The label says there is 81.5 lbs of carbon in the filter. So 15% of 81.5 = 12.225 + 100 = 112.3 lbs. If in 11 months the filter is re-weighed and it weighs less then 112 lbs - it is still good.
There are now products called Duct Air Silencers that will reduce fan/filter noise by 35-40%. They are to be installed after the fan, but the closer to the fan you place them the more effective they will be at dampening the noise.
Lastly, why should a customer choose to buy a CAN filter over another brand?
1. They are made in North America, not imported from China
2. They have more rigid quality standards in place
3. Every filter is checked a minimum of 5 different times for quality during the manufacturing process
4. They use the highest grade carbon CKV4 – it passes rigid brittleness, hardness, and pore size tests. IT IS THE BEST CARBON POSSIBLE FOR REMOVING VOC’S!