4.5 kwh. Assuming that the power of the electric furnace is P (unit: watt) and the working time is T (unit: hour), the electric energy consumption can be expressed by the following mathematical formula: the electric energy is equal to P times T, and the electric energy consumption is the product of power and time. In the problem, P=450W and T= 10 hour, then the electric furnace works 10 hour and consumes 4500 watts.