Quote Originally Posted by Balkey
What are the temperatures in the hut? How old is your activated carbon?
Both excellent questions.
The other I would ask is whether the fan is too strong for the filter, but at that velocity I doubt that is your problem.
One quick fix I would put out there would be to pick up an 'odorsok' which is a relatively inexpensive carbon filter that you can slip over the end of either the 'in' end of your exhaust duct or the outlet. It secures with a drawstring and folds up quite small when not in use. You could then add that as a 'backup' second level of air treatment on those days when you can detect odor.