Honeywell C7189R1004 Wireless Indoor Temperature & Humidity Sensor - White | Smart Home Monitoring for Thermostats, HVAC Systems & Climate Control

We underwent a complete overhaul: new Amana 18SEER, variable ECM air handler, and CTK04 communicating thermostat with builtin RedLink wireless capability. The thermostat location is technically "correct", away from windows/dead zones/etc., but the thermostat was unaware of the difference between our 1st and 2nd floors. Our communicating system adjusts the ECM blower speed according to demand and we were overcooling to generate greater demand to increase blower speeds for the 2nd floor.I bought four of these, put three of them upstairs and the final one in our southerly-facing living room with high ceiling. The displayed temperature changed and the thermostat increased the blower speed immediately -- awesome!Few things I figured out from piecing various documentation together (mostly from the T10 manual) for our ComfortNet/Bridge CTK04 system, generally applies to other Honeywell thermostats too:1. When multiple wireless thermostats are used then the temperature is a *weighted* average, the thermostat is 50%. Meaning that with our thermostat and four wireless sensors, the thermostat was 50% of the average, and each wireless thermostat made up 12.5% of the remaining 50%. I disabled the addition of our CTK thermostat to the temperature average for the cooling season. I will add it back to the average during winter to keep the upstairs from becoming overly warm.2. The thermostats follow a PID algorithm so do not expect an immediate change in the behavior of your system. It will learn how large and for how long temperature deviations exist and, overtime, will correct/anticipate runtime, blower speeds.3. Only one thermostat can be used for dehumidification should the capability exist on your system. Even though I disabled the CTK thermostat *temperature*, I have maintained it as the humidity sensor, and everything continues to work properly.