This depends solely upon your growth setup. If you are using a grow tent that is too big - then you need to get a dehumidifier which can dehumidify a larger volume of air. However, if you’re using a small grow tent then you would be ok using a smaller dehumidifier too. The best dehumidifiers for grow rooms need to be more powerful and the biggest in size because it is easier to dehumidify a tent compared to dehumidifying an entire room.