How Does a Dehumidifier Work?

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Last updated: 
April 23, 2024

How Does a Dehumidifier Work? Understanding the Process and Solving Common Problems


When asked "How does a dehumidifier work?", people are often either curious or frustrated that their dehumidifier isn't working properly. This article explains the process of how a dehumidifier removes excess moisture from the air, detailing each step and providing tips on what to do if the appliance isn't functioning as it should. By understanding how a dehumidifier works, you can maximize its benefits and ensure a comfortable, healthy living environment.

The Dehumidification Process

A dehumidifier works by pulling in moist air and condensing the moisture out of it to dry the air. The unit contains tubing filled with refrigerant, which is circulated by a compressor. The refrigerant first moves to an evaporator, where it collects heat from the air, and then to a condenser, where the heat is released. The purpose of using refrigerant to capture heat from the air around the evaporator is to make the evaporator cold enough for moisture to condense on it. The condensed water then drains into a collection bucket or drain tube, effectively dehumidifying the air .

Dehumidifier Steps and Solving Common Problems

Step 1: The Dehumidifier Pulls in Moist Air

A fan in the dehumidifier pulls humid air into the front of the appliance. If this isn't happening, the most common problem is that the humidistat, which indicates how dry you want the air, is set below the humidity level in the room. Turn it up, like turning up a thermostat until the furnace comes on, to make the dehumidifier start. If you turn it up all the way and nothing happens, the collection tank may be full, prohibiting the unit from turning on. Check and empty the tank if needed. Alternatively, the air may be drier than the driest setting on the humidistat, so the compressor won't start circulating refrigerant, or the fan or electrical components may not be working and require repair.

Step 2: Refrigerant Captures Heat in the Evaporator

If warm air is being blown out the back of the dehumidifier, it is collecting heat as it should. If the fan is running but no heat is being removed from the air, your unit might have a continuously running fan, but the humidistat setting is too low to cause the compressor to come on and start circulating refrigerant. Adjust the humidistat to a drier setting. Alternatively, the dehumidifier might be low on refrigerant, so it's not collecting heat, requiring repair or replacement. If the dehumidifier is working but less effectively than it used to, the refrigerant might be slowly leaking out, necessitating repair or replacement, or the air filter at the front of the dehumidifier might be dirty, reducing the intake of air. Take it out and clean it.

Step 3: The Evaporator Gets Cold and Condenses Moisture

If the unit seems to be running normally but little moisture is being condensed and collected or drained, turn up the humidistat until the compressor starts (you might hear it come on). Check the evaporator and clean it if it is covered with debris, as dirt prevents heat transfer. Also, check to see if the float that descends into the collection tank is stuck in the "up" position, which automatically shuts off the compressor to prevent overflow. If it is, gently pull it down and remove dirt and debris from the float arm to free up its movement.

Step 4: Moisture Drains into the Tank or Drain Hose

If the unit shuts off when the air is still humid, empty the tank if it is full or turn the humidistat to a drier setting. If the dehumidifier leaks, check to see if the float is stuck and not rising as the water rises. Turn off the dehumidifier and gently push the float up, clearing debris from its arm that might be causing it to stick. The drain hole, if it has one, might also be plugged by debris, preventing water from entering the drain line. Search for and clear a clogged drain hole.

Step 5: Warm, Dry Air Comes Out the Back

If the fan is running but the airflow seems diminished, clean the air filter. If the air coming out is cool, review Steps 2 and 3. If the air that comes out smells bad, clean the filter if it is dirty, replace the filter or clean it with an oxygen bleach solution if it is moldy, and empty the tank, cleaning it with an oxygen bleach solution if it is moldy.

Tips for Maximum Dehumidifying

To get the most from your dehumidifier, follow these tips:

  • Check the filter every few days and clean it as needed.
  • If you have a drain hose attachment option, use it to allow continuous operation. If you collect water in a tank, it will shut off when full, and you might not be able to empty it for hours or days. Ensure the hose runs to a floor drain.
  • Keep doors and windows shut to prevent humid air from continuously flowing into the space.
  • Run a vent hood fan when boiling liquid on the stove and the bathroom exhaust fan when taking a shower to remove humidity.
  • In warm weather, run a central AC or window unit to assist with dehumidification. Air conditioning uses the same technology, except that an AC moves warm air to the outside of your home while dehumidifying the indoor air .
  • If the space is below grade and humidity issues persist, contact a foundation specialist about damp-proofing your home's basement or crawlspace.


Many homes have humidity issues that make them uncomfortable and potentially unhealthy due to mold growth. By understanding how a dehumidifier works and following the steps and tips provided in this article, you can effectively remove excess moisture from your living space, creating a more comfortable and healthier environment for you, your family, and your pets.

Relative Humidity LevelEffect
30-50%Ideal range for comfort and health
Above 50%Promotes mold growth and dust mite reproduction
Below 30%Can cause dry skin, irritated sinuses, and static electricity

According to the EPA, maintaining relative humidity levels between 30-50% helps to minimize the growth of mold, dust mites, and other allergens . By using a dehumidifier and following the steps and tips outlined in this article, you can effectively manage humidity levels in your home, promoting a healthier and more comfortable living environment.

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