Dehumidifiers are devices that are designed to remove moisture (humidity) from the air. This dehumidification is necessary to prevent the growth of mold and also for our comfort. (If you already have mold in your home, you can check out our removal guide for advice on getting rid of it.)
There are basically two ways to remove excessive humidity from a home.
The first method is by using chemicals called desiccants which have a high affinity for moisture. Basically, these materials tend to absorb or release water vapor as necessary to reach an equilibrium with the air surrounding them. This method is most often used in commercial and industrial buildings.
For most homeowners this is not a practical solution.
The other method uses a refrigerant system. This works on the principle of vapor condensation. Basically, this means that when the temperature of air is reduced to its dew point, water condenses out of the air and collects on the cold refrigerant coil.
We will only cover the latter method in detail here.
Portable dehumidifiers are a self contained refrigeration system that is designed to control the humidity in a smaller area. There are some disadvantages to this type of unit.
First, these units have a compressor in them that produces heat. This heat is released into the room where the unit is located. This heat then has to be removed by the home's ac system. These units also use more electricity than other units.
The sensor and control on some these units is normally not very accurate. There are two types of controls mechanical and electronic with electronic controls being more accurate.
These units have a rated capacity that is given in pints or liters. That is the maximum amount of moisture the unit can remove from the air in one day. The actual capacity will depend on the home's temperature and other factors.
Most of the units have a built in defrost system. This senses when the coil on the machine is becoming blocked by ice. The machine then melts the ice.
These units require some routine maintenance. The filter should be cleaned every month and the coil should be checked for dirt and cleaned as necessary.
Our dehumidifier ratings will help you to select a brand. Some things to check before buying are that the unit is rated to operate at your expected temperature. (Some units are rated for above 75 degrees F while others are rated for 45F) Units that are designed to operate at 45F are commonly called low temperature dehumidifiers. Also, you need to get the proper size, the proper voltage, and the proper frequency (50hz or 60hz).
A whole house dehumidifier works a lot like the portable unit. The main difference is that it is connected to the central hvac system. This system typically has a built in control that runs the fan and checks the humidity level on a set schedule.
This system also has some disadvantages. These units can be relatively expensive. It also contains a compressor in the home which can add heat to the home and also makes unwanted noise. The heat that is produced must be removed by the hvac system (that can raise your electric bill)They will normally use less electricity than portable units.
The last method uses the existing hvac system. The normal thermostat is replaced with one that also senses the humidity. When the thermostat senses a need to remove humidity, the air conditioner comes on. The blower motor on the furnace comes on at a lower speed than is used for normal operation. This has the effect of lowering the evaporator coil temperature. This removes more moisture than normal.
The disadvantage of this method is that it can result in over cooling of the home. This is especially true if the system is not properly sized. A way to overcome this is by using a two speed air conditioner. This coupled with a furnace with a variable speed blower motor will minimize over cooling. It accomplishes this by running in low speed for humidity removal.