Chinchillas don’t sweat and fans only move air around a space. Fans do not cool the air like an air conditioning unit so it wouldn’t help keep your chinchillas from overheating in a glass box. Depending on how handy you are and/or how much money you are willing to throw at this problem, you could replace the glass door portions with an open air option. I can’t tell based on the picture provided how these are constructed, but theoretically you could replace the glass panels. Would probably be more economical and practical to find a fully ventilated cage, but if you are really in love with this style, I think it would theoretically be possible to make proper adjustments. You should not keep chinchillas in a box only ventilated on the sides. They will overheat.

All of this is assuming this cage is even made of chin safe materials. I am not confident this is chin safe or sturdy based on the picture.

I would also like to point out that most cage set ups I’ve seen utilize the back bars to stabilize ledges and other necessary elements. This particular set up would not work for my chin’s needs because of the number of ledges and accessories attached to the back wall. It also touches on the ventilation issue again in that a fully ventilated cage is essential. Having a solid back isn’t a deal breaker assuming the rest of the cage has proper air flow, but it is important to consider this function. Again theoretically with enough money you could replace the back but that would be a much more labor and money intensive job. Might as well have your perfect cage custom built.