The size of a dehumidifier is usually determined by the amount of moisture it extracts from the air in a 24-hour period. The Association of Home Appliance Manufacturers' guidelines are a good resource in deciding on a correctly sized dehumidifier. Portability is also important, especially for dehumidifiers that will be used in multiple rooms. Ideally, the unit should be lightweight, compact and have rolling casters or carrying handles.

A built-in humidistat is a good feature to have because it allows for the humidity levels to be adjusted. The unit also turns on or off automatically depending on the humidity levels. An automatic shut-off feature prevents the unit from overfilling and saves power.

Storage tank capacity is an important consideration because a larger storage tank does not need to be drained as often. The alternative is purchasing a continuous drainage model, which drains the moisture directly through a hose. Finally, a dehumidifier with a removable or washable air filter is simple to maintain, and helps save money on parts. (Source)