How to Choose the Right Dehumidifier

Dehumidifiers have become an essential appliance for homes and offices. In addition to keeping you comfortable, a dehumidifier can also prevent serious damage that can be caused by excessive humidity in the air.

Humidity is often compared to the muggy, steamy-room feeling that you sometimes get on a summer day. When most people express concern over humidity levels, they're talking about relative humidity. The air can hold a fixed amount of water vapor - depending on its temperature.  Relative humidity is the ratio of actual water vapor currently in the air compared to the total amount it can hold.

Effects of Excessive Humidity

Excessive humidity levels make the air feel heavy, and can be quite uncomfortable. It has also been known to affect people's moods, and can even make you feel sick to your stomach. It can also be dangerous, especially when combined with high temperatures. The humidity can disrupt your body's ability to cool itself, which can lead to various heat-related issues. It can also aggravate allergy symptoms, and lead to more ongoing allergic reactions.

If you think excessive humidity is rough on your body, you should see what it can do to your home! If the humidity levels in your home are high, it can affect the structural integrity of the building. Creaking floors are usually a giveaway that your home's humidity levels are high. It can also damage your home furnishings as well. In addition, excessive humidity can lead to an increase in mold and stains on your ceilings and walls. It has also been associated with musty odors.

If your home seems to be suffering from any of the aforementioned symptoms, then you may need a dehumidifier.

Dehumidifiers are household appliances that help to reduce the humidity levels in the air. Dehumidifiers work by pulling in the moist air from a room, and then removing the moisture from the air before recirculating it back into the room. In effect, through this process, a dehumidifier will lower the humidity level in your home or office. Some more modern dehumidifiers have additional features and functions, including a humidistat.  Humidistats can detect the level of humidity in a room, and allow you to program your dehumidifier to only run when the humidity in a room reaches a specific level.

There are also many different sizes and of dehumidifiers available, so it's important to know what size dehumidifier you need. The two most important factors when deciding on a dehumidifier are capacity and air flow volume.

Dehumidifier Capacity

The size of a dehumidifier is generally based on the amount of moisture extracted from the air in a 24 hour period. Typically, this capacity is measured in pints. Dehumidifiers with a higher capacity can remove moisture from a larger room in a shorter amount of time than units with a smaller capacity. The size of the room you need to dehumidify and the amount of moisture in the air generally will determine the size and capacity of the dehumidifier needed.

The Association of Home Appliance Manufacturers has developed recommended capacity and sizing guidelines based on these factors.

Air Flow Volume

Another measure that can determine the size of dehumidifier you need is the amount of air the appliance can move over a certain period of time. Dehumidifiers measure this in cubic feet per minute, or CFM. CFM is an important measure for dehumidifiers because the unit can only extract moisture from the air that passes through the dehumidifier. In essence, all the air in your room must flow through your dehumidifier in order for the moisture to be removed.

The recommended CFM needed is calculated based on the square footage of the room and the humidity level in the area. The size of the room determines how much air - in cubic feet - needs to pass through the dehumidifier. The level of moisture in the air tells you how many times the air in your room should cycle through the dehumidifier every hour. This s known as Air Changes per Hour, or ACH. The higher the relative humidity in your room, the more often the air should cycle through your dehumidifier, or the higher ACH needed. By estimating the amount of humidity in the air, you should be able to find the recommended ACH: 

• Damp air (60-70% relative humidity) feels clammy or smells musty. This is the typical humidity level in basements and crawlspaces. Recommended ACH = 3
• Very damp air (70-80%) smells of mildew and may leave visible stains on the wall or floor. Recommended ACH = 4
• Wet air (80-90%) is air in which mold and mildew are present, with visible stains and wet spots on the walls or floor. Recommended ACH = 5
• Very wet air (90-100%) is the air in a space where standing water is present. Recommended ACH = 6

To calculate the CFM you need from your dehumidifier, simply multiply the cubic feet of the room by the recommended ACH, and then divide that number by 60 minutes. The resulting number is the CFM your dehumidifier should have.

There are two things to remember when looking for dehumidifiers with a specific CFM in mind. First, if your room requires a higher CFM than you've been able to locate on any dehumidifier unit, you can use multiple dehumidifiers to remove excess moisture from that space. Second, there are no ill effects of using a dehumidifier with a higher CFM than you need. In this case, your unit will simply run less frequently.

If you're looking for more information, be sure to see our guide on How Dehumidifiers Work . For more on choosing the right dehumidifier for your home or office, be sure to check out the Dehumidifier Buying Guide .