At HomeQuestionsAnswered, we're committed to delivering accurate, trustworthy information. Our expert-authored content is rigorously fact-checked and sourced from credible authorities. Discover how we uphold the highest standards in providing you with reliable knowledge.

Learn more...

What is a Dehumidifier?

Stefanie Spikell
Stefanie Spikell

A dehumidifier takes moisture out of the air by condensing it onto a cold surface. Have you ever poured a cold glass of water on a hot, humid summer day? If you have, you have seen the moisture condense on the glass. This is because when air cools, it can't hold its moisture. If you leave the glass on a table long enough, and if the air is humid enough, a big puddle of water will form. The same thing happens in an air conditioner when the moisture in the room condenses on the air conditioner's cold coils. You will notice, if this is a window unit, that water drips out the back of the unit onto the ground. So, a dehumidifier is just an air conditioner that has both its hot and cold coils in the same box. First, a fan draws the room's air over the cold coil of the air conditioner to condense the moisture. Next, the dry air passes through the hot coil to heat it back up to its original temperature.

If you have a room that is air conditioned, it should not need a dehumidifier -- the air conditioner should be doing the dehumidifying for you. But if you don't have an air conditioner, a dehumidifier is at least some help in the heat.

Here are some tips to remember for maintaining your dehumidifier in tip top shape:

  • Don't forget to change the filter once a year so that your machine will run at optimum performance.
  • Clean the water container from time to time to avoid mineral build up in the pan.
  • Inspect the cooling coils for frost or ice build-up, as this can destroy the machine.
  • Don't short-cycle the cooling system — this means not to turn it off and then on again right away. Wait at least ten minutes to let the pressure in the system equalize.
  • Don't set the humidistat higher than necessary or it will run constantly.

Discussion Comments


is that the same effect as when inside a closed car, w/o the aircon turned on, and raining outside? Moist forms on the glass windows on the car?


Why would there be minerals in the water in the pan? As far as I know water that comes out of the air should not contain any minerals.


Since dehumidifier is not a food appliance, I would not think of using that water that collects in the container for anything else, but watering plants possibly.


what is the difference between tempered glass and low-e annealed glass argon filled?


Is the water from a dehumidifier (distilled water) safe to drink or use?


One of my rooms (it is an addition, probably without insulation) gets so humid, especially during winter month, that without a dehumidifier, the floor and walls feel wet to the touch. The moisture in the air gives a feeling of coldness too.

The dehumidifier unit, that I bought a few years ago, is doing an excellent job, keeping the humidity at the desirable level, and also keeping the room warmer. I set the level at a certain percentage, usually 45 or 50,and the unit does the rest.

Every now and then, the container collecting water needs to be emptied, but that is about it. One disadvantage though is that the sound, when the unit is on, is a little too loud. It would be more desirable if the sound could be muted in some way.


How do you build one? Preferably one that can be manually operated when electricity cuts out.

Post your comments
Forgot password?
    • A dehumidifier may be used to take moisture out of the air.
      By: Kellis
      A dehumidifier may be used to take moisture out of the air.
    • An ideal humidity level is about 45 percent.
      By: Are Barstad
      An ideal humidity level is about 45 percent.