Once you draw the air thru the carbon filter its "clean". How long of duct you blow it through after the filter means nothing as far as odor. That space you are going to blow the clean air into goes where ? Remember, fans make noise. And if you are going to need to keep door open you are going to get odors anyways. If only a few plants I am going to say the filter will last around 6 or so grows. I have grown a C99 cross that was to be low-no odor, orange smell or something, and thats bullshit. You can smell it, I am convinced it doesnt matter what strain it is.

I have honestly been thinking about your grow and trying to come up with a idea for ventilation, and HEAR me thru on this. Is there ANYWAY you could cut this door you are talking about needing to keep open and installing a 12"x12" darkroom louver ? Then you could keep a window open, and when your fan kicks on you would be sucking air thru a light proof vent, so no worry about light leaks.............After the air comes in, all gets drawn thru the filter and exhausted into the "space" you are showing ???????? At least that way we are eliminating the reakage from gettin in the rest of the house cause door is open. I know its not ideal, but I am trying to brainstorm to help you out here..........

My point is you are buying all this equipment, so lets use it the way its intended to be used so you can get the best results.

Is the above idea an option or do I go back to the drawing board ?

b0nger