A dehumidifier is much like a vacuum cleaner, the only difference being it sucks out moist, humid air from your room instead of dust. It sucks in the humid air from one end, takes the moisture out of it and then blows back dry air into the room.

The moisture that is removed from the humid air is collected in a tank (condensed in the form of water) needs to be emptied from time to time.
Dehumidifiers remove moisture from the air with the help of HVAC or Heat Ventilating Air Conditioning unit, which itself is like a refrigerator.

Let us get into the technical side and figure out how dehumidifiers work.
Dehumidifiers work in one of the two ways. They work either by absorption/adsorption, in which the moisture is absorbed or adsorbed on the surface of a drying material which needs to be removed upon saturation. Or by refrigeration.

If dehumidifiers work on the principle of absorption or adsorption which works in the following way:

Moist air is drawn into the dehumidifier from a room through a duct.
The air then moves through a large rotating wheel which is made of a water-absorbing material that helps in removing the moisture content.
The air is drawn by a fan, that is operated by an electric motor.
Dry air is blown back into the room.
The wheel that absorbs or adsorbs the moisture rotates through a heated air space and blown-dry with the help of hot air.
This hot air then passes through a fan which is also powered by a separate electric motor and is blown out through an exhaust duct.
This whole arrangement is usually controlled by a thermostat and humidity sensors, giving you the control to make the room as hot and dry as you want.

Dehumidifiers working on the principle of refrigeration have a different approach. These dehumidifiers work in the following way:

Warm and moist air is sucked through a grill arrangement which is present on one side of the machine.
The electric fan draws the air inwards. This warm air then passes through freezing pipes which have coolant getting circulated in them.
As the air passes over these pipes it gets cooled down and the moisture in it gets condensed and turns into liquid water that drips down off the pipes.
The moisture-free air then passes over a heating element and warms up the air.
The moisture which has now turned into water drips into a collecting tray at the bottom of the machine.
Some dehumidifiers have a separate electrical mechanism to indicate that the tray is full, while others just have a float that indicates the level of water in the tray.

You can avoid the confusion in choosing the best dehumidifier for your home if know exactly what to look for in a dehumidifier.

There are many factors that contribute in choosing a suitable dehumidifier for your home, geographical location is one of them. Purchasing a dehumidifier involves choosing the size and type which will eliminate humidity and moisture issues from your home.

Following points will help you buy a suitable dehumidifier for your home:

Sizing
Size of the area that you will be dehumidifying is the first thing you need to consider while buying a dehumidifier. Do not forget to include the height of the room in the equation, because you will be drying of the entire room space and not just along the floor.

Geographical location
Apart from the size of the room you wish to dehumidify, it is the geographical location that matters while buying a dehumidifier. If you are resident of Gulf regions, Florida, and Texas, you might need a dehumidifier almost throughout the year. Also, people living on the west coast of the United States would need a dehumidifier during the winters, because this is the time it rains the most in those areas. To conclude, you might require large capacity dehumidifier for up to 8 to 10 months.

Air temperature and current humidity in the room
Most dehumidifiers work fine in temperatures above 24 degrees Celsius and above. You might need a specialty low-temperature models for dehumidifying rooms that are below 20 degrees Celsius. It is important that you know the severity of the moisture issues in your room. Rooms with humidity higher than 60% will need a dehumidifier.

The desired level of humidity
It is recommended that lowering the humidity of a room below 50% will eliminate the potential hazards of mold and dust mite population, which can damage the property of your home. The lower you set the humidistat of your dehumidifier, the longer it will operate. If you have musical instruments at your home (such as guitars and pianos) it is recommended that you maintain the humidity below 45%.

Energy Star rating
When it comes to buying electrical appliances, people always look for energy star rating of the appliance. The more the energy stars the appliance has, the more the energy saving it does. However, in the case of dehumidifiers, the efficiency is measured in terms of the number of points that it removes per kilowatt of electricity. So, next time, when you go shopping for a dehumidifier, look for this rating.