How Does A Dehumidifier Work

By: Evan Scoboria, Last updated: June 28, 2023

Dehumidifiers remove excess moisture from the air, preventing mold growth, reducing allergens, and protecting your home's structure. In this article, we'll dive into the inner workings of dehumidifiers and explore how they effectively control humidity levels.

How Does A Dehumidifier Work

Understanding Humidity and its Effects:

Humidity, the measure of air's water vapor content, influences weather patterns and human comfort. This atmospheric component is quantified as relative humidity (RH), representing moisture relative to maximum capacity at a given temperature.

Excessive humidity, often exceeding 50%, impedes sweat evaporation, causing perceived warmth, discomfort, and clamminess. Respiratory difficulties can escalate under such conditions, favoring mold, mildew, and dust mite proliferation - common triggers for allergies and asthma. Prolonged exposure results in wall and window condensation, potentially harming building integrity.

Conversely, low humidity, typically below 30%, intensifies the air's coolness and can lead to discomfort, such as dry skin, eye irritation, and respiratory issues. It can also induce static electricity and damage wooden items by promoting shrinkage and cracking.

Maintaining indoor humidity within a 30%-50% range is crucial for comfort, health, and safeguarding possessions. This balance is achievable by applying dehumidifiers and humidifiers, which modulate indoor humidity.

The Basics of Dehumidifiers

Dehumidifiers, instruments controlling indoor humidity to remain within a 30%-50% healthful and comfortable range, draw excess moisture from the air. Their application forestalls potential issues such as mold formation, allergen spread, and property damage.

Here's a more in-depth look at the basics of dehumidifiers:

  1. Size and Capacity: Dehumidifiers display variations in size and capacity to accommodate distinctive spaces. Portable versions cater to small rooms, while larger models manage basement or whole-house dehumidification. Capacity is gauged in daily pint-quantity of moisture removal.

  2. Functionality: All dehumidifiers, irrespective of size, absorb environmental air, extract moisture, and return dry air to the room. The collected water is stored in a reservoir requiring periodic emptying or direct drainage via a hose with continuous drain dehumidifiers.

  3. Control Features: Dehumidifiers often include controls for setting humidity levels, which trigger automatic cycling of the device to maintain this level when reached. Additional features may include operational timers, fan speeds, and automatic shut-off upon water reservoir filling.

  4. Energy Efficiency: Energy consumption varies among dehumidifier models, with Energy Star-rated units offering superior efficiency.

  5. Maintenance: Optimal dehumidifier performance necessitates regular maintenance, including water reservoir emptying, air filter cleaning, and occasional coil cleaning. Certain models provide indicators for these maintenance tasks.

Main Components of a Dehumidifier

A dehumidifier comprises four main components facilitating moisture removal from the air: a fan compressor, a refrigeration system, a reheater, and a reservoir or drain.

  1. Fan Compressor: This motor-driven unit initiates the dehumidification process, drawing air into the device, allowing continuous treatment of incoming air.

  2. Refrigeration System: Critical for compressor-based dehumidifiers' operation, this system involves several elements:

    • Compressor: This component pressurizes the refrigerant, raising its temperature.
    • Condenser: The condenser cools the refrigerant, transforming it from a gas to a liquid state, releasing the heat it absorbed earlier.
    • Evaporator: The evaporator further cools the air, which reduces the air's ability to hold moisture, leading to condensation.
    • Expansion Device: This part regulates the flow of the refrigerant into the evaporator, allowing the refrigeration cycle to continue.
  3. Reheater: Post moisture extraction, the air might be significantly cooled. The reheater returns the air to its initial temperature before it is released back into the room, preventing it from becoming too cold.

  4. Reservoir or Drain: This is the final collection point for condensed water. Some dehumidifiers incorporate a removable reservoir or bucket, requiring manual emptying upon filling. Others employ a drain hose for continuous water drainage into a sink, drain, or outside, enabling uninterrupted dehumidifier operation without manual emptying.

Desiccant dehumidifiers substitute the refrigeration system with a desiccant material absorbing air moisture. A heater within the device warms the desiccant material, releasing the trapped moisture into the reservoir or drain.

What Does a Dehumidifier Do?

A dehumidifier serves the primary purpose of reducing excessive moisture in the air. In doing so, it addresses several problems and offers multiple benefits for your home and health:

  1. Prevents Mold and Mildew: These fungi thrive in damp conditions, and by reducing humidity levels, a dehumidifier creates an inhospitable environment for them, thus preventing their growth.

  2. Curbs Dust Mites: Dust mites, a common cause of allergies, also flourish in high humidity. Lowering the moisture in the air helps keep these tiny creatures in check.

  3. Protects Your Home: Excess humidity can cause damage to your home's structure and furnishings, promoting wood rot and damp patches on walls and ceilings. By reducing the moisture in the air, a dehumidifier helps protect your property.

  4. Improves Air Quality: By reducing humidity, dehumidifiers help limit the concentration of airborne allergens and pollutants, improving indoor air quality.

  5. Enhances Comfort: High humidity can make the air feel sticky and warmer than it is. A dehumidifier can make your home feel more comfortable by reducing the clamminess of the air.

  6. Eliminates Musty Odors: The musty smell often associated with damp basements and other areas of your home is caused by mold and mildew growth. Since dehumidifiers help prevent these fungi, they can effectively eliminate these unpleasant smells.

  7. Promotes Health: By reducing allergens and improving air quality, dehumidifiers can alleviate symptoms of allergies and asthma, promoting a healthier living environment.

  8. Helps Your Air Conditioner: A dehumidifier can also help your air conditioning system run more efficiently by reducing humidity. The air conditioner won't have to work as hard to remove moisture and cool the air, which can extend its lifespan and reduce energy consumption.

The Science Behind Dehumidifiers

Dehumidifiers operate on the straightforward principle of condensation. Understanding these appliances necessitates knowledge of relative humidity - a metric indicating moisture content in the air relative to the maximum it can hold at a given temperature. High relative humidity implies near-saturated air.

Dehumidifiers aim to lower relative humidity by eliminating excess air moisture. They do this by drawing in room air and cooling it. Cooling the air reduces its moisture retention capacity, leading to the condensation of some moisture into water droplets.

Two primary dehumidifier types, refrigerant (or compressor) and desiccant, utilize different air cooling mechanisms:

Refrigerant Dehumidifiers cool an internal coil using refrigerant. Humid air flowing over the coil condenses its moisture, collected in a water tank. The dehumidified air is then reheated to its initial temperature and released back into the room.

Desiccant Dehumidifiers operate differently, using a desiccant material for natural moisture absorption. Humid air passing through the dehumidifier comes into contact with a rotating desiccant wheel that absorbs moisture. The wheel then moves into a separate heated chamber, releasing the moisture into a collection tank. The air is subsequently cooled before being discharged back into the room.

Both types effectively lower a room's relative humidity, creating an environment less suitable for allergens like dust mites and mold, enhancing overall comfort.

Types of Dehumidifiers

There are two main types of dehumidifiers: refrigerant (also known as compressor-based) and desiccant. Refrigerant dehumidifiers use a refrigeration system, as described earlier, to cool the air and condense moisture. They are generally more energy-efficient and better suited for larger spaces or higher humidity levels like basements or main living areas. On the other hand, desiccant dehumidifiers use a moisture-absorbing material called a desiccant to remove moisture from the air. They are typically quieter and more effective at lower temperatures and humidity levels but can be less energy-efficient.

Refrigerant Dehumidifiers

Refrigerant, or compressor-based dehumidifiers, are the most common type for residential use. They work by utilizing a refrigeration cycle similar to that of an air conditioner or refrigerator. Here's a more detailed step-by-step explanation of how these types of dehumidifiers work:

  1. Air Intake: The process begins when the fan compressor draws humid air from the room into the dehumidifier. This allows the machine to intake and process the moisture-laden air.

  2. Cooling Coils: Once the air is inside the dehumidifier, it's directed over the cooling coils. These coils are filled with refrigerant that absorbs heat from the air as it passes over them, and the absorption of heat causes the air to cool down.

  3. Condensation and Collection: As the warm, humid air cools, it's unable to hold onto the same amount of moisture. This causes water to condense on the cold coils. The condensed water droplets drip into the dehumidifier's reservoir or are directed out of the unit through a drain hose.

  4. Reheating: Finally, the cooled air is passed over the warm side of the cooling coils. This reheats the air to its original temperature before being released into the room. The discharged air is drier and less humid than before, which helps reduce the room's overall humidity.

Refrigerant dehumidifiers are particularly effective in warmer, more humid environments. This is because the capacity of air to hold water vapor increases with temperature, which means that these dehumidifiers can extract more moisture from warmer air. Additionally, they tend to be more energy-efficient than desiccant dehumidifiers because they use refrigerated heat to reheat the air.

Desiccant Dehumidifiers

Desiccant dehumidifiers operate differently from refrigerant models. Instead of using a refrigeration cycle to remove moisture from the air, they employ a unique moisture-absorbing material known as a desiccant. Here's a more detailed explanation of how desiccant dehumidifiers work:

  1. Air Intake: Similar to refrigerant dehumidifiers, the process begins when the fan draws humid air from the room into the dehumidifier.

  2. Desiccant Material: The air is passed over a rotating wheel or drum coated with desiccant material. This material has a high affinity for water and readily absorbs moisture from the passing air.

  3. Releasing Dry Air: Once the desiccant absorbs the moisture, the drier air is released back into the room. This helps to lower the overall humidity in the space.

  4. Regeneration of the Desiccant: Over time, the Desiccant material becomes saturated with water and needs to be regenerated or dried out. This is done by passing a separate warm air stream over the desiccant, which causes it to release the absorbed moisture. This moisture is then collected in a reservoir or drained away from the unit.

Desiccant dehumidifiers can be particularly effective in cooler temperatures and lower humidity environments. This is because, unlike refrigerant dehumidifiers, their performance does not depend on the dew point temperature of the air. They can also operate at lower noise levels, making them suitable for bedrooms or other quiet spaces. However, they can be less energy-efficient than refrigerant models, requiring additional energy to heat the air used to regenerate the desiccant.

Frequently Asked Questions

  1. How do I know if I need a dehumidifier? If your home frequently feels damp, has a musty smell, or shows visible signs of moisture, such as condensation on windows, water stains on walls or ceilings, or mold growth, you might benefit from a dehumidifier.

  2. How often should I run my dehumidifier? This depends on the humidity level in your home. In very humid conditions, you might need to run it continuously. In less humid conditions, a few hours a day may be sufficient. Modern dehumidifiers have a built-in hygrometer that measures humidity and automatically turns on and off to maintain a set humidity level.

  3. What should the humidity level be in my home? The Environmental Protection Agency recommends maintaining 30% and 50% indoor humidity. Levels above 50% can promote mold growth, dust mites, and other allergens.

  4. Where should I place my dehumidifier? You should place it where excessive humidity is problematic, such as in a basement, bathroom, or kitchen. It should be positioned away from walls and furniture for good air circulation.

  5. How do I maintain my dehumidifier? Regularly empty the water collection tank to prevent mold and bacteria growth. Also, clean the air filter as recommended by the manufacturer. Depending on the model, you may also need to clean the cooling coils.

  6. Does a dehumidifier use a lot of electricity? Dehumidifiers use electricity, but the amount varies based on the model and size. Larger dehumidifiers will use more energy. However, reducing humidity can also make your air conditioner work more efficiently, potentially reducing energy consumption.

  7. Can a dehumidifier cool a room? Dehumidifiers are not designed to cool a room like an air conditioner. They remove moisture from the air, making the room feel less sticky and more comfortable in humid conditions. However, dehumidifiers produce heat as they operate, which can slightly increase the room temperature.

  8. What is the lifespan of a dehumidifier? The lifespan of a dehumidifier can vary greatly depending on the quality of the unit, how often it is used, and how well it is maintained. You can expect a dehumidifier to last between 3 and 5 years. Some well-maintained units can last even longer.


In conclusion, dehumidifiers are quite essential in maintaining a healthy living environment. They function based on scientific principles to extract excess moisture from the air, ensuring the relative humidity in your home is comfortable and healthy. By doing so, dehumidifiers help prevent issues such as mold growth, allergens, and damp conditions. However, understanding how your dehumidifier works and maintaining it properly can enhance its efficiency and lifespan. Refer to your user's manual and consult with professionals when necessary for the best results.