Do leaving heater switch on consume electricity?

Yes, leaving a heater switch on consumes electricity, even if the heater is not actively heating. Many heaters have standby modes that draw a small amount of power to maintain settings or sensors. Additionally, if the thermostat is set to a temperature that the room is already at, the heater will not operate, but it will still use some electricity. To save energy, it's best to turn off the heater when it's not needed.