Geothermal heating has been used since the time of the Roman Empire as a way of heating buildings and spas by utilizing sources of hot water and steam that exist near the Earth's surface. The Roman Empire was the post-Republican phase of the ancient Roman civilization, characterised by an autocratic form of government and large territorial HVAC (pronounced either "H-V-A-C" or occasionally " H-vak " is an Initialism or Acronym that stands for " Heating In Architecture, Construction, Engineering and real estate development the word building may refer to one of the following Any man-made The term spa is associated with water treatment which is also known as Balneotherapy, Spa towns or Spa resorts offering such treatment or the medication Water is a common Chemical substance that is essential for the survival of all known forms of Life. Uses A Steam engine uses the expansion of steam in order to drive a Piston or Turbine to perform Mechanical work. The lithosphere (IPA, from the Greek λίθος for "rocky" + σφαίρα for "sphere" is the solid outermost shell of a rocky Planet.  The ultimate source of geothermal energy is believed to be from the radioactive decay that occurs deep within the Earth’s crust. Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation.  Some areas, including substantial portions of many western states (U. S. ), are underlain by relatively shallow geothermal resources.  Similar conditions exist in Iceland, parts of Japan, and other geothermal hot spots around the world. These resources can be classified as low temperature (less than 90°C or 194°F), moderate temperature (90°C - 150°C or 194 - 302°F), and high temperature (greater than 150°C or 302°F). Where such geothermal resources are available, it is possible to distribute hot water or steam to multiple buildings. This technique, long practiced throughout the world in locations such as Reykjavik, Iceland, Boise, Idaho,, and Klamath Falls, Oregon  is known as geothermal district heating. For the Greater Reykjavík Area see the Greater Reykjavík Area. Iceland, officially the Republic of Iceland ( ( Ísland or Lýðveldið Ísland ( Boise (ˈbɔɪsi is the capital and most populous city of the U The State of Idaho ( is a state in the Pacific Northwest region of the United States of America. Klamath Falls is a city in Klamath County, Oregon, United States. Oregon ( is a state in the Pacific Northwest region of the United States. District heating (less commonly called teleheating) is a system for distributing heat generated in a centralized location for residential and commercial heating requirements
In recent years, the term geothermal heating has frequently been used to refer to the heating and cooling that can be achieved through the use of a geothermal heat pump. A geothermal heat pump system is a heating and/or an Air conditioning system that uses the Earth's ability to store heat in the ground and water Thermal This technique is generally for residential use. It involves a refrigerant liquid being pumped through pipes in the ground, heating the liquid. A refrigerant is a compound used in a heat cycle that undergoes a Phase change from a Gas to a Liquid and back This liquid then is brought back into the house, and the heat exchanged. The same technique is used to cool the house.
Geothermal heat pumps take advantage of the natural constant temperature of the earth.  During winter when the ground temperature is warmer than the air above it, geothermal heat pumps use the earth’s soil (or groundwater) to recover the earth’s heat. In contrast, an air-source heat pump will remove heat from the cold outside air and thus requires more energy. An air source heat pump is a type of Heat pump which use the outside air as a heat source or heat sink to heat or cool
In the summer months, geothermal heat pumps deliver heat to the same relatively cool soil (or groundwater) rather than delivering it to the hot outside air. As a result, the heat is pumped over a smaller temperature difference with a geothermal heat pump and this leads to higher efficiency and lower energy use. 
The conditions necessary for water to circulate to the earth’s surface are present in, less than 10 percent of Earth’s land area.  Therefore, geothermal heating is not always a feasible option. Hot dry rock is a method of capturing the heat embedded in these dry areas. Hot Dry Rock Geothermal Energy (HDR is a type of Geothermal power production that uses the very high temperatures (approx 200 Celsius that can be found in rocks First, high-pressure water is pumped down a borehole and through the rocks to break them apart. Water is then pumped from the surface through the ground and the broken hot rocks. This causes the water temperature to rise. The hot water is returned to the surface through a second well and is used to drive turbines for electricity or to provide heat.  The water is then returned to the ground and the process repeated.
There was an experimental facility built in 1974 in Fenton Hill, New Mexico that studied hot dry rock. A well was drilled 11,500 feet into rock at 430 °F to demonstrate the feasibility of hot dry rock technology. The water returned to the surface at 360 °F after being pumped down the well at 80 °F. The plant produced as much as five megawatts of power, proving that energy from hot dry rock can be extracted for practical applications. 
Geothermal energy is a type of renewable energy that encourages conservation of natural resources. According to the U. S. Environmental Protection Agency, geo-exchange systems save homeowners 30-70 percent in heating costs, and 20-50 percent in cooling costs, compared to conventional systems. A geothermal heat pump system is a heating and/or an Air conditioning system that uses the Earth's ability to store heat in the ground and water Thermal  Geo-exchange systems also save money because they require much less maintenance. In addition to being highly reliable they are built to last for decades and can add considerably the resale value of a structure.
Geothermal energy is one of the few renewable energy technologies that—like fossil fuels—can supply continuous, base load power. Fossil fuels or mineral fuels are fossil source Fuels that is Hydrocarbons found within the top layer of the Earth’s crust. Baseload (also base load, or baseload demand) is the minimum amount of power that a utility or distribution company must make available to its customers or the amount  In the past, electricity costs from geothermal facilities were noticeably high. Over the past few decades, these costs have steadily declined. Some geothermal facilities have noticed a 50 percent reduction in the price of electricity over the past 25 years. New facilities can produce electricity for between 4. 5 and 7. 3 cents per kilowatt-hour, making it competitive with new conventional fossil fuel-fired power plants.  The future for the direct use of geothermal resources is becoming more attractive as prices continue to drop. It is predicted that geothermal heating will continue to become a more popular option for homes and businesses seeking long term cost and energy savings.