Dehumidifier Basics
Capacity
Dehumidifier capacity is usually measured in pints per 24 hours and is determined by two factors: the size of the space that needs to be dehumidified and the conditions that exist in the space before dehumidification. Use the chart below to estimate the capacity you are looking for.
| Condition without Dehumidification | Area (Sq. Feet) | ||||
|---|---|---|---|---|---|
| 500 | 1,000 | 1,500 | 2,000 | 2,500 | |
| Moderately Damp (space feels damp and has musty odor only in humid weather) | 10 | 14 | 18 | 22 | 26 |
| Very Damp (space always feels damp and has musty odor. Damp spots show on walls and floor.) | 12 | 17 | 22 | 27 | 32 |
| Wet (space feels and smells wet. Walls or floor sweat, or seepage is present.) | 14 | 20 | 26 | 32 | 38 |
| Extremely Wet (laundry drying, wet floor, high load conditions.) | 16 | 23 | 30 | 37 | 44 |
Source: Association of Home Appliance Manufacturers (AHAM)
Water Removal Options
Most dehumidifiers use a removable plastic bucket and warning lights to indicate when the bucket is full and needs to be emptied. There is typically an automatic shutoff when the bucket is full, so you won’t have to worry about the bucket overflowing.
Most dehumidifiers come with a fitting that allows you to hook a hose directly to the bucket, which can then be directed into a floor drain or sump pump, so there is no need to empty it.
Placement
Most dehumidifiers have top-mounted air discharge and can be placed against walls, but if you do not have top-mounted discharge, make sure the dehumidifier is located away from walls and furniture, so that air can circulate freely around the unit. This will result in better operation of the product.
Doors and windows to the space being dehumidified should be closed while the unit is running. This will ensure that the space is dehumidified as efficiently as possible.
Locate away from sources of dust and dirt (like woodworking equipment), which can clog coils and grills.
Observe all manufacturer warnings regarding electrical safety. In particular, never set up water drainage or disposal near electrical circuits or devices. Make sure the dehumidifier is connected to a properly grounded outlet. Keep drain hoses away from electrical cords and connections.
If you are planning to use a hose to drain the dehumidifier’s water bucket, make sure the unit is located near enough to the floor drain or sump to avoid the need for a long and unwieldy hose. Don’t create a tripping hazard!
Do not be alarmed if the air temperature directly around the unit is warmer than in surrounding areas. As a dehumidifier removes moisture from the air, it slightly warms the space around it.
Operating Temperature
If the space being dehumidified has temperatures that typically fall below 65 degrees (F), you may want to consider buying a product that is specified for use at lower temperatures.
Frost can form on the condensing coils if the air temperature drops below 65 degrees, and may negatively affect the performance of the product by causing the compressor to cycle on and off repeatedly without removing moisture from the air. If this happens, the unit should be switched off and allowed to defrost before it is turned back on. Some dehumidifiers come with an antifrost sensor, which will automatically turn the unit off if the air temperature drops below a certain point.
Qualified ENERGY STAR models are available that are rated for use at temperatures as low as 42 degrees.
Relative Humidity (RH) and Humidistats
Humidity, the amount of moisture or water vapor in the air, is most often talked about in terms of Relative Humidity (RH). RH is the amount of water vapor actually present in the air compared to the greatest amount of water vapor the air can hold at that temperature. The optimum RH level for a building is generally considered to be between 30% and 50%. Anything above this range may promote bacteria growth. (In colder climates, during the heating season, humidity levels should be in the range of 30% to 40% RH to prevent window condensation.)
Many dehumidifiers include a built-in humidistat, a device that allows you to set the desired RH level that you would like for the room. Once the room reaches the desired RH level, the dehumidifier will cycle on and off automatically to maintain the level.
If your dehumidifier does not have a built-in humidistat, or has a humidistat that does not show RH levels purchase a hygrometer (a gauge that measures relative humidity) separately and hang it near the dehumidifier. The hygrometer will measure RH levels, and enable you to monitor when to turn the dehumidifier on and off.
Energy Factor
The energy efficiency of dehumidifiers is measured by its energy factor, in liters of water removed per kilowatt-hour (kWh) of energy consumed or L/kWh. In general, a higher energy factor means a more efficient dehumidifier. Energy factors can be found on the product list (EXCEL, 36.5KB).