In extremely cold weather conditions where the inside thermostat is set to 27 C and the outside temperature is -20 C, your 1200 square ft house might lose heat through the walls at a rate of 4000 W. How much energy might you lose in one week? Electric heat can be 100% efficient. At 10 cents per kilowatt-hour how much would it cost to heat your house for one week under such cold conditions?