Yeah it pretty much depends on the filter/space and overall environment....

I got myself a carbon fiber filter not too long ago to try it out.... Well it worked for the first couple months but after having to wash it every month, it's effectiveness wore thin.... Replaced it with a Phresh Filter.... I asked the store owner the same question about longevity....and he responded that the Phresh Filter can be emptied and refilled with fresh carbon if the smell starts coming through....maybe every 4-6 months....

I've had the bigger newer filter going for 4 months now and have yet to smell my garden outside of the cab....and now use the fiber filter for intake....

CGI::::::