It fit perfectly in my previously installed Honeywell thermostat. The instructions for ISU's were very helpful and with a little research, I was able to properly select and set the thermostat advanced menu options. It performs well and given the main reason I purchased the WIFI version, which was to support changing the settings remotely, I will save 3+ times the cost in the first year of use.
Love being able to change mode, set temperature, turn on off and circulate from anywhere. This allows us to travel and control the HVAC System, With the easy-to-use app