You will likely need to refill or replace your CO2 tank every two to four kegs, depending on the size of your canister and kegs used. You can do it yourself using an air compressor or have them refilled at a welding shop or homebrew or beverage supply store. This can be one of the most costly and inconvenient aspects of using a kegerator, so make sure that you find a reputable place nearby or learn to DIY it before you decide on a kegerator.