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The proper use of humidifiers and indoor air quality are directly related, particularly in winter conditions when outdoor humidity levels drop. While air quality is often thought of as simply a consequence of either infiltrating pollutants originating outdoors or from sources inside of the home, humidity is an element in this process. Certain humidity levels tend to create an indoor environment that supports specific air quality conditions. Making the connection between humidifiers and indoor air quality can keep your home healthier and its occupants more comfortable.

Low Moisture and Indoor Air Quality

The federal Environmental Protection Agency states that indoor humidity should range between 30 percent and 60 percent. Levels below that can be a result of simply low outdoor humidity during winter. But indoor humidity also can be lowered by forced-air furnaces operated during winter. Standard-efficiency gas furnaces draw air for combustion from inside the house. Household air drawn into the combustion chamber becomes dry from exposure to the burner flame. The continuous circulation of forced hot air throughout the house also removes water vapor. Combined with naturally drier winter air infiltrating into the interior of the home, interior humidity may drop below recommended levels.

When indoor humidity is low, the negative affect of certain contaminants on indoor air quality is magnified. At humidity levels below the recommended range, these pathogens and pollutants proliferate:

  • Viruses. While it was long believed that cold and flu viruses were related to moist conditions, more recent research has conclusively shown that these pathogens actually thrive in dry air below 35 percent relative humidity.
  • Respiratory illness. The American Academy Of Allergy, Asthma and Immunology states that respiratory irritation, a precursor to respiratory illnesses such as asthma and allergic rhinitis, increases as humidity levels fall below 40 percent.
  • Ozone production. Ozone is a colorless gas component of air pollution; prolonged inhalation of ozone causes lung damage and throat irritation. At indoor humidity levels below the EPA standards, ozone production increases.

Other byproducts of low indoor humidity include comfort-related issues such as the fact that dry air feels colder, causes itchy, dry skin, and subjects occupants to painful static shocks when touching certain surfaces. Because dry air doesn’t hold as much heat, energy costs to keep the home warm may increase. Low humidity also can be the cause of structural issues such as shrinkage in wooden floors and cabinetry.

Evaluating Humidifiers and Indoor Air Quality

Mechanical methods to increase humidity can be divided into two groups: portable room humidifiers and whole-house humidification.

  • Portable humidifiers. These units, commonly sold on the shelves of home centers, generally produce sufficient humidity to treat the air in a single, enclosed room. They utilize a refillable reservoir that requires daily filling with water and incorporate a blower fan to disperse humidity into the living space. Portable humidifiers require regular maintenance including cleaning to discourage bacterial growth in components that contain standing water. The noise level from portable units, while generally less than a window A/C, is still noticeable in enclosed rooms. Most experts recommend placing a portable humidifier in bedrooms for maximum hours of exposure to occupants.


  • Whole-house humidifiers. Installed inside the HVAC ductwork in the home, a whole-house unit treats the entire volume of indoor air as it repeatedly circulates through the ducts. The whole-house humidifier is permanently plumbed to a household water supply line, so no user input is required to fill the reservoir. A thin layer of water is dispersed over a perforated panel in the duct airflow, adding water vapor to the air. The humidifier is activated by a digital humidistat located in the living quarters, usually on a wall just like the HVAC thermostat. Desired humidity settings can be input by the user, and the unit will then continuously monitor indoor air and activate the water flow in the humidifier as necessary. Maintenance is generally limited to annual cleanings by an HVAC technician. Because it utilizes the existing furnace airflow to circulate humidified air, the energy expense of an additional blower is avoided.

Other Measures

You can help sustain indoor humidity levels by sealing the house against the infiltration of dry winter air. Cracks and gaps in the structure, as well as worn weatherstripping around windows and doors, allow outdoor air into the home that may be below desired humidity levels. A well-sealed house also tends to more effectively accumulate indoor humidity generated by household activities like cooking and bathing.

For more information on humidifiers and indoor air quality this winter, in Sarasota please contact us at Aqua Plumbing & Air.

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