I always wondered why no one has designed a Peltier cooler/heater for car seats. One polarity you get cooling, the other heating.

 

The JLR cooled seats only use a peltier/TEC device for cooling the air pumped through the seat, and use traditional resistive wires for the heating as they are more efficient and add very little to the build cost. Some vehicles do use them for both heating and cooling though - the Ford Flex is an example. Maybe the forced air allows them to operate at a lower temperature but similar comfort levels?