Ventilation in Humid Climates

Ventilation can refer to the process of bringing air in or exhausting it from a building. Bath fans and kitchen hoods are ubiquitous and can expel indoor air, but bringing in outdoor air effectively requires a bit more planning and care.

Bringing outdoor air into the home helps dilute harmful substances inside homes, including volatile organic compounds (VOCs) from cleaners, flooring, paints, and furniture. Outdoor air also dilutes carbon dioxide, which humans and pets exhale naturally (though house plants can also help control indoor carbon dioxide content). Ventilation also helps keep our indoor environments pretty close to the outdoor environment (given that the outdoor air environment is healthy and free of smog, smoke, etc.).

However, when we bring outdoor air inside, we need to watch out for the relative humidity. When the outdoor relative humidity is high, then the outdoor dew point is also high. Bringing that air into a cooler space will wring that excess moisture out of the air and make it “rain” all over the surfaces in the home, leading to insect problems and microbial growth. Older Floridian homes (“Cracker” houses) were designed before A/C was widespread, and many of these homes were “loose” with large breezeways and windows that were meant to be left open on hot days. Houses nowadays are much tighter, and VOCs and carbon dioxide can exist in much higher concentrations indoors.

ASHRAE Standard 62.2 requires buildings to bring in outdoor air to dilute and purify indoor air. However, Florida’s high dew points present a challenge for bringing in outdoor air. Since the outdoor dew points are high, we often need to rely on filtering and dehumidifying outdoor air via a ventilating dehumidifier. A filter alone is not good enough to remove harmful spores and particulates from the air. ERVs and HRVs tend to work well in other parts of the country but have their limitations in humid climates. Ventilating dehumidifiers tend to be among the most practical solutions for tight homes in humid climates.