Summary
ASHRAE Standard 62.1-2016 recommends that relative humidity in occupied spaces should be less than 65% to create conditions less conducive for microbial growth. The EPA recommends maintaining indoor relative humidity between 30% and 60%. Operating humidity standards should always be maintained when human occupancy is present, however HVAC systems can be turned off or reduced during non-operating hours. It is important to note that turning off HVAC systems during non-occupancy may save energy, but depending on external conditions, more energy may be required to meet operating conditions once occupancy begins again.