A home heating system maintains the indoor temperature at 20 C. The outside temperature is 0 C. A furnace burns natural gas to heat a 1:4 mixture of outside and inside air. The resulting air is at a temperature of 40 C. Draw a Sankey diagram of this system for a furnace that loses 20 percent of heat in its exhaust. You may ignore changes in the density of air with temperature. The fuel value of natural gas is 46 MJ/kg.