Abstract: An environmental temperature control system comprises one or more thermostats (10). The or each thermostat is integrated into an electronic control circuit having an external temperature sensor means (12), with a floor temperature sensor means (14) and a room ambient temperature sensor means (16) provided for the or each thermostat. All of the temperature readings from the sensor means in the or each thermostat are intended to be fed to a processing means to control the floor temperature of an underfloor heating system in one or more rooms or areas of a building.