To operate the heater, plug it into an electrical outlet and place it in an area where heat is desired. The illumination of the light at the male end of the plug indicates the heater is receiving power and will heat when the temperature falls below 38°F. To prevent the heater from accidently being turned off, there are no switches or knobs. The thermostats are hermetically sealed and nonadjustable. When the ambient temperature reaches the thermostat set point, the heater will automatically turn on and will not turn off until the pre-set temperature is reached. Please allow ONE FULL HOUR for the heater to acclimate when being relocated from a warm environment to a cold one (i.e. going from a garage to a boat). The heater’s large mass requires considerable time to cool enough to activate the thermostat.