Humidification adds moisture to the air, while dehumidification removes it.
Humidification
Adds moisture to dry air, using humidifiers. Used in winter and for health, with a target indoor humidity of 30% to 50%.
Dehumidification
Removes moisture from humid air, with AC or dehumidifiers. Used in basements, summer and to prevent mold.
Why it matters
Humidity above 60% promotes mold and dust mites. Below 30% dries skin and airways.
Devices
Humidifiers: cool mist, warm mist. Dehumidifiers: compressor and desiccant types.
Physical process
Humidification increases the amount of water vapor in the air, and dehumidification removes it. Relative humidity is the amount of moisture in the air compared with the maximum at that temperature.
Indoor targets
The EPA recommends keeping indoor relative humidity between 30% and 50%. Above 60% promotes mold and dust mites. Below 30% causes dry skin, static electricity and irritated airways.
Humidifier types
- Evaporative, ultrasonic, steam and whole house systems. Whole house humidifiers connect to the HVAC system.
Dehumidifier types
- Refrigerant (compressor) dehumidifiers cool air below the dew point so moisture condenses on coils. They work best above 65 degrees F.
- Desiccant dehumidifiers use absorbent materials and work at low temperatures.
- Air conditioners also dehumidify as a side effect.
Capacity
Dehumidifiers are rated in pints removed per day, such as 20 to 50 pints. A 500 to 1,500 square foot space needs about 20 to 35 pints, depending on dampness, according to Energy Star guidelines.
Industrial uses
Controlled humidity matters in museums, hospitals, food storage, electronics manufacturing and pharmaceutical production.
Measuring
A hygrometer measures relative humidity and costs about 10 to 20 dollars.
Health
High humidity favors mold and dust mites, which worsen allergies and asthma. Low humidity can make viruses such as influenza survive longer in the air.
Maintenance
Empty the water tank, clean filters and keep coils clear. Clean humidifiers regularly to avoid microbial growth.
Process and targets
Humidification adds water vapor to air to raise relative humidity, and dehumidification removes water vapor to lower it. The EPA recommends keeping indoor relative humidity between 30 and 50 percent, and no higher than 60 percent, to limit mold, dust mites and discomfort. Humidifiers include evaporative, ultrasonic and steam types, and dehumidifiers either use refrigeration coils that condense water or desiccant materials that absorb it. Dehumidifier capacity is rated in pints per day, for example 30 to 50 pints for a basement of 1,000 to 2,500 square feet.
Uses and care
Humidifiers help in dry winter air and with dry skin and nosebleeds, while dehumidifiers help in damp basements, humid climates and after water damage. Industrial users such as data centers, hospitals and museums control humidity tightly. Measure with a hygrometer. Empty and clean water tanks often, since standing water breeds bacteria and mold. Clean dehumidifier filters and coils, and drain the bucket or connect a hose. Too little humidity can irritate airways, and too much promotes mold growth that may worsen asthma and allergies.
Based on data from the EPA and the Department of Energy
