Slow cookers can be energy-efficient because their heating element relies only on captured heat and uses low currents to heat the food. Slow cookers take less time to cook, so they are one of the best energy-efficient cooking appliances. The power consumption of a slow cooker for 8 to 9 hours is about 1300 W. That's less than 2000 watts for a 2000-watt oven, which will cook at 350F for 60 min. You can also decrease evaporation.