Secondary Author(s)

Withers Jr., Charles

Report Number




Humidity; Buildings; HVAC; Dehumidification


In a hot and humid climate such as Florida, 'snowbirds' that leave their homes for extended summer periods need guidance on effective and energy efficient methods of humidity control. Experiments were performed in seven residences to evaluate various approaches to humidity control, including providing no mechanical system control. A humidity target was identified to maintain indoor relative humidity (RH) at 65% or lower most of the time. Providing no mechanical conditioning (letting the building 'float') yields relative humidity at 65% or below during hot and sunny weather in some homes, but not during cloudy weather. Setting the AC system thermostat at 85°F or 83°F yielded lower than required RH during hot and sunny weather, but it yielded insufficient RH control during cloudy weather. Furthermore, AC energy use peaks during the utility's peak demand period. Running the AC system for two hours a day (3-5 AM) yielded effective and energy efficient RH control. Operation of a dehumidifier on timer control or humidistat control provided good results with the lowest overall energy use. Operation of the space heating system to maintain 89°F (which yields 65% RH when the outdoor dew point temperature is 75°F) provides reliable RH control, with good energy efficiency during hot weather (assuming a heat pump as the heating system). However, during cooler weather, the space heating approach consumed considerably more energy. Operation of the space heating system based on humidistat control provides reliable RH control and eliminates the excessive energy use which occurs during cooler weather with the constant 89°F setting.

Date Published



Original Publication: Cummings, J. and Wither, C., "Assessment of the Effectiveness and Energy Efficiency of Humidity Control Approaches in Vacant Florida Homes", Sixteenth Symposium on Improving Building Systems in Hot and Humid Climates, December 15-17, 2008, in Dallas, TX.

Local Subjects

Buildings - Dehumidification; Humidity; Buildings - HVAC


FSEC Energy Research Center® Collection



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