Hi. I work at a Petsmart, but not one that sells ferrets. The cages are designed to have air filtering through, to reduce the stink and circulate the air. If the system is working correctly, it does keep air circulated. Fresh air would be better, in my opinion. When you have rats or ferrets in those cages, as well as guinea pigs, the cages need to be cleaned every day in order for the odor to be down. The cages are cleaned once a week but "spot cleaned" when they need it at busier stores. The problem with this system is that it keeps the tanks very humid, not good for the ferrets at all. The temperature inside the cages can also rise without you knowing, if the fan breaks, let's say (or the controller). This is why I check on the animals periodically. I like Petsmart's version MUCH better. Plus, at least then, the people can know that ferrets DO have an odor, good or bad. I think that, more than any other reason, has kept a significant number of people from buying them who otherwise might have from a cage where the poo odor was masked. Laryssa [Posted in FML 5661]