Geothermal systems can also be enhanced by recycling old oil and gas wells for geothermal use. It is cheaper to change these wells for heat mining than to drill new holes. These wells do not allow for physical contact between the water and the heat source. These wells are made out of two cylinders: a bigger one and a smaller one. The smaller one fits inside the bigger one and is where the heated water is pumped out from. Water in inserted between the lining of the inner pipe and the outer one. Due to the lack in direct contact with the hot rocks as well as some heat loss from lack of a good insulating material, the energy output is not as high as in ordinary geothermal systems.