Review on 🌡 WH8040 1%~99% RH HM-40 Type Digital Air Humidity Control Controller 110V by Justin Sherman

I use this humidistat in the fresh air system in my wine cellar. It is wired in series with two thermal switches that measure the inside and outside temperature to turn on the fans that bring in cold air from the outside. This works great in my San Francisco Bay Area climate, which has cool summer nights. Of course, you don't want to bring in air that is too humid, otherwise you'll get mold, so I limit the humidity in the basement with this controller. This controller works in either humidifier or dehumidifier mode and is adjustable in 1% increments, making it very flexible. It has programmable hysteresis so it will not turn on/off at the set point. It offers a Type-C relay shutter capable of driving loads up to 10A (120VAC). You can easily connect the hot side of the AC circuit to control a fan, humidifier, or dehumidifier. The translation of the instructions (yes, it's from China) could be improved a bit, but if you read it a few times, you'll understand. I connected an ohmmeter to the relay and experimented with the humidity set point to activate the relay. Wet/dry modes work in reverse. The moisture sensor is very sensitive, readings are measured in tenths of a percent. I really like this little controller for my application. It's been in use for a few days now, so I'm in no way judging its long-term reliability!