In HVAC controls, a device that responds to humidity and can control a system is a

• A. Humidistat
• B. Thermostat
• C. Hygrometer
• D. Barometer

Answer: (A)

In HVAC controls, a device that responds to humidity and can control a system is the humidistat. A humidistat senses relative humidity and uses that reading to actuate equipment such as a humidifier or dehumidifier, keeping the room at a desired humidity level. This is different from a thermostat, which senses temperature to control heating or cooling; a hygrometer, which only measures humidity without controlling anything; and a barometer, which measures atmospheric pressure. So the humidistat is the component that both reacts to humidity and can drive the HVAC equipment to maintain the set humidity.