The most important factor is how much water the particular unit will remove in a certain period of time. Next in importance is the size of the water discharge tank or the availability of direct draining. You don’t want to spend a lot of time emptying a small tank so identify a model with the largest storage tank available. Then look at maintaining the unit. Filters must be cleaned and/or replaced on a regular schedule, so check filter types, cost and availability before investing. Check out the noise level in the store to see how loud the unit is when it runs. Look for the smallest, most energy efficient model capable of dehumidifying your particular space. All in all, a dehumidifier is a good investment when you’re faced with the unpleasantness that often results from excessively humid air.