Geothermal heating is the direct use of
geothermal energy for heating applications. Humans have taken advantage of
geothermal heat this way since the Paleolithic era. Approximately seventy countries made direct use of a total of 270
PJ of geothermal heating in 2004. As of 2007, 28
GW of geothermal heating capacity is installed around the world, satisfying 0.07% of global primary energy consumption.
Thermal efficiency is high since no energy conversion is needed, but
capacity factors tend to be low (around 20%) since the heat is mostly needed in the winter.