It depends on your needs. My walk-in is in my office which I keep at 70-72, so I won't have a need for a cooling unit in there. If however the need does come, a small portable cooling unit is all that it will take. Depending on size of the room, the coolers they use for cooling small wine cellars would work, they are rear facing so the exhaust does not enter the room.The question I have is how to install a cooling unit. I wonder if I could take a wine cooler and gut it and put it into my humidor project?