A device for regulating temperature, a thermostat may control a heater, furnace, or vent fan.
Merriam-Webster Online Dictionary
thermostat (noun) an automatic device for regulating temperature (as by controlling the supply of gas or electricity to a heating apparatus) , also a similar device for actuating fire alarms or for controlling automatic sprinklers
transitive verb
to provide with or control the temperature of by a thermostat
Regulator, temperature controller, heat manager, climate adjuster, thermal sensor
