| summary=A heat exchanger is used to transfer energy to the potable water from the fluid being heated in the solar collector}}
A heat exchanger is a device built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact. They are widely used in space heating, [http://www.appropedia.org/Refrigeration refrigeration], [http://www.appropedia.org/Air_conditioning air conditioning], power plants, chemical plants, petrochemical plants, petroleum refineries, natural gas processing, and sewage treatment. One common example of a heat exchanger is the radiator in a car, in which the heat source, being a hot engine-cooling fluid, water, transfers heat to air flowing through the radiator (i.e. the heat transfer medium).