You are better off buying a higher capacity dehumidifier than a unit that is too small. Smaller units may run continuously without bringing the humidity down to optimal levels. Higher capacity humidifiers also can handle spaces that may be excessively damp from clothes dryers or dishwashers, which add moisture to the air. Keep in mind that if the outdoor climate is humid, it will increase indoor humidity levels. If you live in a humid region, you may want to choose a higher capacity dehumidifier than what the square footage indicates.

Choose a humidifier with automated controls for monitoring and setting relative humidity levels. The optimal relative humidity in a home should be between 40 percent and 50 percent in summer and 30 percent and 50 percent in winter. Dehumidifiers with built-in hygrometers measure relative humidity and display the number. An adjustable humidistat allows you to dial a desired humidity level and the unit will automatically maintain it. If the dehumidifier you choose does not have these settings, you may want to invest in a hygrometer to hang next to the dehumidifier. The device ranges in price from $10 to $60 and will measure the indoor humidity so you know when to switch the unit on and off.

Consider the unit’s bucket size. Dehumidifiers with larger tubs or drip pans need to be emptied less often. But expect to pay a little more for the convenience. A rule of thumb is that the more water a dehumidifier can extract and hold, the more it is likely to cost. Shop around because prices can vary. Often the best deals are in the spring. Expect to pay about $140 for a 25-pint dehumidifier and $225 for a 70-pint dehumidifier. Dehumidifiers with front-loading buckets are easiest to empty manually.

Most portable dehumidifiers are equipped to be self-draining and come with a drain-hose connection. A garden hose may do. But the dehumidifier will need to be placed in an area where the hose can empty water, such as into a basement floor drain or above the sink in your laundry room.

Opt for a dehumidifier that can function at low temperatures. Unless you live in a climate that is warm year-round, consider a unit with an automatic defrost feature. The heat-exchange coils on a dehumidifier can frost over when indoor temperatures drop below 65–60 degrees Fahrenheit. This will cause your dehumidifier to work less efficiently or stop removing moisture altogether. Although you may pay a little more for the automatic defrost feature, it will spare you the expense of replacing a unit damaged from iced coils. Look for a unit that is Energy Star certified to 45–40 degrees F.

Other key features to look for in a dehumidifier include:

Quiet operation. Noise can be a nuisance, especially if the dehumidifier is in or near a bedroom. Dehumidifiers with two-speed fans run quietly at lower humidity levels. They also save on energy costs. It’s not a bad idea to test a dehumidifier’s noise level before you make your purchase.

Mobility. Make sure your new dehumidifier comes with casters so it can be rolled from room to room. A long power cord will enable you to put the unit anywhere you want it.

Automatic shutoff. An overflow protection valve will cause the unit to switch off when the tub is full and needs to be emptied. This is a key feature to have on any model you choose. Some dehumidifiers have indicator lights to show when the bucket is full.

Energy efficiency. Dehumidifiers that carry the Energy Star label will save money on utility bills. Dehumidifiers certified with the government-sponsored label are guaranteed to use less energy yet run efficiently.

Washable filters. Some models have filters that protect the coils from dirt and dust. Make sure you can easily remove the filters and wash them, a task you should do about twice a month. This will allow you to replace the filters less often.