A humidistat (sometimes also called a hygrostat) is a small measurement instrument or device that helps to monitor and maintain the set or preferred relative humidity in the air. A humidistat it often included as a humidity monitoring and control feature on portable humidifiers or on combined air cleaner/humidifier units, to help you better manage your home's moisture level.
A Humidistat Goes Beyond Monitoring
A hygrometer also gives you a reading of the room's humidity level, making it a convenient monitoring tool, but it differs somewhat from an onboard humidistat. A humidistat goes beyond monitoring, helping to restore and maintain an optimum or preferred humidity level. So a humidistat usually has a dual purpose. It's not unusual though to find stand-alone small humidistats that act more like hygrometers, simply for monitoring purposes. Sometimes these two terms (humidistat and hygrometer) are used interchangeably.
Though this humidity level feature is ideal especially when factored into a humidifier or other air quality appliance, it tends to be limited in its readings by sheer design. That is not to say that it's not helpful. It provides the current humidity level right at the air quality appliance, then adjusts to control moisture output till the preferred level is reached—but only in its surrounding space. Ten feet away, the accurate moisture reading might be different, than the one right at the unit.
How to Use a Humidistat
When a humidifier is operating, it's a given that the air right around it will be more humid, than the air a few feet away. Though this is a nice feature to have and the measurement reading is important to know, it may not be realistic of the entire room's moisture level.
That's where a hygrometer placed at the other end of the room, can confirm the humidistat's efficiency and whether you should adjust it slightly higher or lower to cover the entire space. Maintaining a proper moisture balance in your home is crucial to preventing over-humidifying, which can result in mold spores, or at the other end of the spectrum, having a very dry room which would be uncomfortable.
You'll pay a little more for the humidistat feature on an appliance and though limited, it is important information to have, since the control aspect can be considered a safety feature, reducing the risk of over-humidifying the room. Combine that with a companion hygrometer and you can better manage the room's moisture level.
The recommended home humidity level is within the range of 45 to 60%. A dehumidifier is required to remove excess humidity. A humidifier is used to add moisture to a room. These two appliances can be considered home essentials. Factors that influence their necessity are climate, weather, temperature, heating or cooling effects on air comfort and other conditions specific to the home itself, such as a continually damp basement.