Mountain air filters are the gold standard of carbon filters and have been so for 14 years. Designed to give maximum quality, performance and longevity. No other filter has been able to last more than 3 years of constant use. They offer superior airflow compared to other filters, due to the very low density but high mechanical strength of activated carbon used. Mountain air filters remove 99% of everything under 20 microns from the air in one pass, Including dust, lint, mold spores and organic odours. Activated Carbon Filters used in hydroponic grow rooms are the most effective means of cleansing the extracted air to remove any odours. These filters work by a method called adsorption (as opposed to absorption) Simply put, adsorption means that odour-causing molecules stick to the inside of the activated carbon without the carbon itself increasing in size. In the same way that a sponge can only hold so much water before it is completely saturated, carbon filters too reach a point where they are unable to extract any further odour-causing molecules from the air. In addition, the adsorption characteristic of the carbon means that heavier molecules can displace lighter ones - freeing the lighter molecules to flow out into the atmosphere. For growers, this means that they will detect odours leaving their extraction ducting before the filter reaches the end of it's useful life. This is known as the breakthrough point. Premium Carbon Filters such as the Mountain Air range not only have a useful life much longer than competeing brands, they also retain odour-causing molecules more effectively, which leads to a later breakthrough point. Users of these filters can rest assured knowing that their extraction air will be odourless right up until it's time for a new filter. Overlay the pressure drop graph of your extraction fan on the graph and you will find an intersection (crossover point) between the two operating curves. Tracing down from this intersection you can read the airflow of a particular fan / filter combination. CFM = M3/Hr ÷ 1.699 INS WG = Pa ÷ 249. Fan Types: You can use two main fan types with the Mountain Air® Filter (Mixed-Flow & Centrifugal Fans).