Indoor humidity refers to the amount of water vapor suspended in the air inside a home. Managing this level is necessary for maintaining a comfortable and healthy living environment. When the air holds too much moisture, it creates a muggy feeling that makes the temperature feel warmer, leading to discomfort. High humidity encourages the growth of mold and mildew, which causes musty odors and can damage materials like wood, drywall, and paint finishes. Addressing this imbalance requires identifying the source, measuring the current level, and employing preventative and mechanical solutions.
Understanding Ideal Humidity and Measurement
The first step in managing indoor moisture is determining the current level and establishing a target range. The ideal relative humidity (RH) level for indoor spaces falls between 40% and 60%, though many aim for 45% to 55% for optimal comfort and material preservation. RH measures how saturated the air is with water vapor compared to the maximum amount it can hold at that specific temperature.
To accurately monitor this level, a simple device called a hygrometer is necessary, which measures the RH percentage in the air. Placing this device in the main living area or a potentially damp space provides the data needed to assess the moisture problem. The hygrometer is an important tool for confirming when the air is too damp or when corrective actions have been successful.
Controlling Indoor Moisture Sources
Many common household activities introduce significant amounts of moisture into the air, making source reduction the most immediate and cost-effective strategy.
Kitchen and Bathroom
When cooking, using the range hood exhaust fan is highly effective at pulling steam and water vapor directly out of the kitchen environment. Covering pots and pans while boiling water also minimizes the steam released into the surrounding air. In the bathroom, run the exhaust fan during a shower and for at least 15 to 20 minutes afterward to fully vent the saturated air. This extended run time ensures moisture is completely removed rather than settling on cool surfaces and condensing.
Laundry and Other Sources
Laundry activities are a major source, requiring clothes dryers to be properly vented to the outside. Air-drying clothes indoors should be avoided, especially in small or poorly ventilated rooms. Minor sources also contribute to the overall moisture load, such as indoor plants or uncovered aquariums, which release water vapor through transpiration and evaporation.
Plumbing Leaks
A persistent, localized humidity problem may be caused by a plumbing issue. Check under sinks and around appliances for small, slow leaks. Repairing a dripping faucet or a pinhole leak immediately prevents water from evaporating into the home’s air over time.
Using Mechanical Equipment to Remove Moisture
When source control is insufficient to maintain the ideal RH, mechanical equipment provides the necessary active removal of water vapor from the air. Dehumidifiers are specifically designed for this purpose, operating by drawing air over a cold coil to condense the moisture into liquid water, which is then collected in a reservoir or drained away. These units are rated by their capacity in pints per day, and proper sizing is determined by both the square footage of the space and the existing humidity level.
Portable dehumidifiers are suitable for localized problems in basements or single rooms, while whole-house units can be integrated into the home’s HVAC system for comprehensive moisture control. Regular maintenance, including cleaning the filter and ensuring the reservoir is emptied, is necessary for efficient operation.
The central air conditioning system also plays a significant role in dehumidification. As the AC unit cools the air, it passes the air over the cold evaporator coil, which causes water vapor to condense and drain away. This dehumidification process is most effective when the unit runs for longer cycles. An oversized unit cools the space too quickly and shuts off before it has run long enough to adequately remove the moisture from the air, leaving the home feeling cool but clammy. Ensuring the AC system is correctly sized for the home’s cooling load and maintaining clean filters and coils allows it to perform its dual function efficiently.
Addressing Structural and Airflow Issues
Long-term humidity control requires addressing the building’s structure and airflow to prevent moisture entry and condensation.
Sealing the Envelope
Sealing air leaks around the building envelope is important, as humid outdoor air can infiltrate the home through gaps around window frames, door casings, and utility penetrations. Using caulk and weatherstripping to close these unintended openings reduces the amount of moisture-laden air that the mechanical systems must process.
Managing Ground Moisture
In basements and crawl spaces, moisture often migrates directly from the damp soil into the home’s air and structure. Installing a heavy-duty vapor barrier, typically thick plastic sheeting, directly on the ground in a crawl space prevents this ground moisture from evaporating into the air above. Proper ventilation or full encapsulation of the crawl space then works with the barrier to manage any remaining moisture.
Ventilation and Insulation
Ensuring adequate attic ventilation is also necessary to prevent warm, moist air from the living space from condensing on the underside of the roof sheathing during colder months. A continuous flow of air through soffit and ridge vents helps keep the attic temperature closer to the outside temperature, preventing condensation that can lead to structural damage. Proper insulation helps keep interior wall and ceiling surfaces above the dew point, preventing surface condensation and subsequent mold growth.