Geothermal Heating and Cooling

How does geothermal heating and cooling work?

Geothermal energy utilizes the relatively stable temperature of the earth that is buried and stored a few feet under its surface. Geothermal energy can potentially be harnessed in the front or back yard of your home.

The geothermal loop, one aspect of geothermal, is being installed in the ground. Courtesy DOE – NREL

Geothermal energy is harnessed from the earth.

One of the three main aspects of a geothermal system, is the series of pipes that are buried in the ground. These pipes store and transfer the relatively constant temperature the lies under the surface of the ground.

Regardless of the season or the degree of the outside temperature, the temperature of the earth a few feet underground remains constant.  Where I live in Western Colorado, this temperature is 56 degrees Fahrenheit.  This can differ depending on the latitude and climate of your specific location.

Over time, a substantial energy saving can be gained by using geothermal energy to heat and cool a building.  This is because energy is not used or burned to produce heat, instead, energy is used to move heat through a system.

When compared to the cost of heating and cooling a residence with propane, using geothermal heating and cooling can cut up to 2/3rds of the cost.


Diagram of a geothermal loop located underground – Courtesy of

Both large institutions as well as smaller private residences can benefit from the utilization of geothermal energy as a heating and cooling energy source.

(Side note: Geothermal energy is an extended beneficiary of the passive solar element of the Earth’s ability to store and absorb the sun’s heat in its large planetary mass. Thus, theoretically it can be debated as an extension of passive solar heating and cooling.)


There are the 3 main components of a geothermal system:

1. The Loop
The loop is located outside the building, typically buried in the ground. The loop houses a liquid that absorbs the energy of the stable temperature that exists underground. A liquid, usually water or water blended with a refrigerant (glycol antifreeze solution) runs continuously through the entire length of the loop. The geothermal loop can be installed in a vertical or horizontal orientation (see below). It is usually composed of a type of high density polyethylene pipe.

Residential Heat Pump – Courtesy of DOE-NREL, credit: Warren Gretz

2. Geothermal Heat Pump
Also referred to as a ground source heat pump (GSHP) it is located within the building and transfers or utilizes the heat energy from the warmer or cooler temperature of the liquid solution coming from the loop to heat or cool the house.  Because it is transferring energy from a stable temperature (58 degrees) in the winter, when the air outside the house is cold, the heat pump pulls the warmer temperature that is gained from the ground and uses it to heat the building. (This is possible because all temperatures above -200 degrees Fahrenheit carry heat. While -200 degrees Fahrenheit sounds very cold to me, heat can still be extracted from temperatures above that amount. Luckily, the temperature of the ground being utilized for geothermal is well above that threshold.)

In the summer, when the outside air is hot, the loop provides a place for the warmer temperature to be discharged.  By the time the solution has run through the extent of the loop, it has been cooled and returns to cool the inside temperature of the house.

The geothermal heat pump functions similar to how a furnace functions, for example, it transfers the heated or cooled air from the loop to the duct work of the building.  Its filter also needs to be periodically replaced.

3. Distribution System
This is the duct work within the building that distributes the heated or cooled air throughout the building.  In contrast to a forced air system that periodically disseminates blasts of air, a geothermal heating or cooling system is constantly pumping air.

Option to add to the system – Hot Water Heater

A “desuperheater” can be added into a geothermal system to heat domestic hot water.  In the summer when heat is being drawn from the house, the heat can first be discharged in the domestic hot water heater before it otherwise would be dispelled in the ground loop.

An award winning residential geothermal system in Oklahoma City.  Courtesy of DOE-NREL

While geothermal heating and cooling is more energy efficient than a traditional forced air system, the cost of installing a geothermal system can cost significantly more. The extra cost spent up front, however, can be returned in the years that follow.

“Even though the installation price of a geothermal system can be several times that of an air-source system of the same heating and cooling capacity, the additional costs are returned to you in energy savings in 5–10 years. System life is estimated at 25 years for the inside components and 50+ years for the ground loop. There are approximately 50,000 geothermal heat pumps installed in the United States each year.”

– Energy Efficiency and Renewable Energy, U.S. Department of Energy,


Choptank Elementary School in Cambridge, Maryland, Courtesy of DOE – NREL

“In 1997, Choptank Elementary School in Cambridge, Maryland began using a GeoExchange system to efficiently heat and cool 45,000 square-feet.

It expects to save $400,000 in energy and maintenance costs over the next 20 years. Choptank Elementary School was the first school in Maryland to use a GeoExchange system.

The school is supplied by 41 ceiling-mounted GeoExchange units located above the classrooms and hallway ceilings. Three other units supply the gymnasium, cafeteria, and small conference rooms. The ground loop is buried beneath the school’s playground. It consists of 1-inch diameter pipes sunk in 100 vertical boreholes, each 275 feet deep. The system’s heating/cooling capacity is 157 tons.”

– Courtesy DOE – NREL, Lingo supplied by the Geothermal Heat Pump Consortium

The geothermal loop system is often installed vertically or horizontally. The decision to use a vertical or horizontal loop lies in the area of land that is available to encase the loop. In order to install a horizontal loop, it is said that there should be at least 1 acre of land available. Less land area is needed to install a vertical loop. The vertical loop can have pipes run at 3, 4 and 5 feet under the ground.


Here is a basic diagram of a horizontal loop, diagram courtesy of DOE

Most of the geothermal loop systems installed are closed loops.  T

his means that the water – antifreeze solution is within the closed system of the loop.

A closed loop system can also be installed within or near water, because a large body of water will also have a constant and stable temperature.



Water can also be utilized as the stable temperature energy source, diagram courtesy of DOE

Open loop geothermal systems can incorporate water from an outside source. These types of systems must also have an additional layer of filters installed and are not recommended for residences.   If water is used, it must be in an area where the bottom layer of liquid does not freeze.

After a geothermal system is installed, the residence usually disconnects propane or other type of heating.


geothermal vertical exchange

Less land is needed for a vertical loop, diagram courtesy of DOE

Electricity is still needed to operate the heat pump. The overall electricity usage and hence cost associated with electricity will typically rise, but will tend to be a lower amount than the original cost paid to the previous utility.

One of the first large scale geothermal applications at the Oregon Institute of Technology. Courtesy DOE-NREL, credit: Mary Smothers

Here is another example of a geothermal heating and cooling application at the Oregon Institute of Technology campus

“The Oregon Institute of Technology has been using a geothermal district heating system since 1964, making it the first modern system. Today, the system heats 11 buildings (600,000 square feet), provides domestic hot water, melts snow on 2300 square feet of sidewalk, and even cools five buildings (277,3000 square feet) during the summer. The district heating system saves around $225,000 each year in heating costs, as compared to the previous fuel oil boiler system.”

– Courtesy DOE-NREL

Other Notable Snippets on Geothermal Energy

The terminology of geothermal can be confusing because it has been used to refer to any type of energy obtained from under the surface of Earth, thus geothermal can refer to hot springs, which are located intermittently throughout the world, or can refer to the harnessing and utilization of the constant relative temperature of the ground to heat and cool buildings.  The information in this article dealt with harnessing the stable temperature of the ground for geothermal energy.

Before installing geothermal, it is recommended to make sure that the building is properly insulated.

The overall size of the loop depends upon the average kilo watt hour (Kwh) energy usage of the building.

Geothermal does not create any surplus of energy for a grid-tie in situation, whereas active solar can generate surplus energy.

Geothermal energy relies on electricity to power the heat pump.  If there is an electrical power failure, unless a type of back up electricity is installed, the geothermal heating and cooling system will stop working.

The costs for installing geothermal are significant because of the amount of piping for the loop that must be installed in the ground.  Costs for upkeep of a geothermal system are minimal, however, it is a possibility that a leak could occur within the loop.  Geothermal, however, is a renewable and sustainable energy source that relies on the constant temperature of the earth.

Thank you to the Delta-Montrose Electric Cooperative for answering my questions about geothermal. DMEA has a program called GeoExchange that helps with the installation of geothermal heat and cooling pump systems for their members.

Geothermal, along with passive and active solar, wind, ocean – wave, hydro and biomass are different types of potential energy sources that can be harnessed as a more sustainable and renewable energy sources.

19 Responses

  1. Kevin Loughran says:

    Hello I
    Thank you for your publication, I just came across it looking for ways to geothermal cooling a house in the tropics, Thailand to be specific.
    Could you please refer me to any information .
    Thank you

  2. It’s great to know that a geothermal system could cut your heating and cooling costs by 75% compared to its propane counterpart. My husband and I plan to have a new vacation house constructed soon. I’ll share this information with my husband because I think a geothermal system would be a great choice for our new home. Thanks.

  3. Tim says:

    Awesome. Thanks, Sam! I was getting annoyed with the lack of a coherent explanation as I read through the comments. I appreciate that you took the time to provide the details.

  4. Sam C says:

    To clarify how the temperature is raised for those who didn’t understand the above comment:

    There are two isolated loops that are only adjacent at a heat exchanger. The ground temperature is captured in the fluid in the exterior loop at 58*F and is transferred to the interior loop through convection at the heat exchanger. A compressor/evaporator are used to compress vapor created by the evaporator. That compression gives off energy in the form of heat. The starting temperature of the interior water is 58* (since it grabbed heat from the exterior loop in the heat exchanger) and the heat produced by this evaporator/compressor process can raise that temp up to ~120*F. To control the temperature you control the flow rate and the valve position to the evaporator or your regulate the compressor output. You then use a fan to blow air across that now very hot water and you have heated air at 72*F or more.

    When you want to cool you reverse the flow of the heat pump so that the interior water temperature of say 76*F (ambient + some picked up heat along the interior pipes) now goes through the heat exchanger to reduce the temp. Let’s say the heat exchanger got the temp down to 69*F. It may also need the evaporator to get cold enough because the hotter the water is the harder it is to exchange all the heat. In that case that vapor being given off is cool. (Kind of like in the summer when it is 80*F outside and you wipe a moist towel over your arm you will feel your arm get cool as the water evaporates.) That chills the water in the interior loop even more and you then blow air across that cold water and you have AC.

    In other words there is a secondary system that takes 58*F and raises or lowers it to the desired temperature unless you go very deep in the ground. Then it gets a little different.

  5. Joseph Baker says:

    I am building a new house. I am using composite ICF construction, and hydronic in-slab heating/cooling. Primary source of heat energy will be wood-fired boiler-stove, with electric water heater as backup. It will also employ a heat-storage tank in addition to regular electric water heater. My house will be supplied with potable water from a well. I came up with an idea for free heat I call the Poor-man’s heat pump. Don’t know if it will work, so I am researching, perhaps you can help. Here’s the idea: my research indicates that the average soil temperature here in western-Washington is about 8 degrees Fahrenheit higher than the average temperature of well water.

    My thought is that instead of installing the shortest-possible water line, which is the usual approach, instead create a ground loop in the water supply line between well and house. This theoretically could harvest that 8 degrees of temperature from the soil and give my heating and DHW system an 8 degree advantage. It would be like lowering the thermostat for your heating and DHW by 8 degrees. That is about 12% of the energy needed to heat all that water to operating temperatures. Is there any obvious flaw in my thinking? If not, about how long would that water line need to be to harvest that heat?

    • Keya Lea says:

      Wow. Your idea sounds amazing. If carried out, would be pretty cool. (Ha, didn’t mean that pun.) But really, it seems that most geothermal applications are closed loop, but I have heard of open loop geothermal heating/cooling. It seems that it was done more frequently in the past, but most of the movement has been toward closed loop. It’s possible to do. Let us know if it works out!

  6. jerk mcgee says:

    In case others are still confused about how a ground temp of 58 can get a room to 72, just think about how your fridge works. It runs on electricity and electricity alone can only produce heat. A refrigerant is used to cool the fridge down to below freezing temperature even though your house is almost certainly not below freezing. So the heating your home works in a similar way but in reverse. If you want to understand the science behind it, you’ll need to read up on latent heat, and heat of fusion and vaporization. These are typically taught in HS chemistry but, if you live in America, that class might have been replaced with bible studies so you should just focus on having faith in the process.

  7. William says:

    I’m curious as to how effective Geothermal is at cooling. A comment was made earlier of how to drop 58 much lower to achieve cooler air. If the inside temp is 20* and below ground is 58* then the liquid would pass through the piping and warm instead cool, that means the the temp going into the piping has to be warmer than the temp under ground.

    • Keya Lea says:

      Yes, the difference between the temperatures is the degrees that needs to be heated or cooled. Because of its relatively constant temp, not as much energy is needed. Geothermal energy is used to both heat and cool buildings.

  8. Jim De Carli says:

    Can you please recommend a HVAC contractor that installs geothermal heat pump systems in Orange County, California?

  9. Barb says:

    I am planning on building a 1600 sqft single story (lofted ceilings open design for livingroom, dining room, and kitchen in northern NY. My design uses passive solar energy…the basement and frame is constructed of icf. I’m thinking that the geothermal heating and cooling system would not be as cost effective for me as I’m already well insulted. Your thoughts????

  10. Ray Fox says:

    You did not answer the previous person’s question as to how to get the heat blowing from the exchanger from 58 deg. to 75 deg. You still need a form of energy be it electric heat, natural gas or diesel to get the temp to a comfortable level…but then why introduce 58 deg. liquid into an air exchanger if you can introduce room air to it which is maybe 70 deg.???

    • Keya Lea says:

      Sorry that seemed unclear to you Ray. A heat pump is used. There are two main types as shown above. Using the example of raising the air from 58 to 75, notice that is a difference of 17 degrees Fahrenheit. A geothermal heat pump has a similar function to a heater that you may have in your house, but it only needs to raise the temperature 17 degrees. Often an additional energy source is used to raise the smaller temperature difference. It uses less energy, and is an overall saving on electricity – because less is needed. Hope that helps. Here’s a link to Wikipedia that might help you:

  11. George Peper says:

    Say the ground temperature is an average of 58*, the outside temp is 20*. You pump the water (fluid) down into the ground and accomplish the thransfer so the water returns to the house heated to 58*, 0nly not hot enough to heat a cool room, it needs to be 72* to 80* sometimes, maybe more, how is the liquid brought up from 58* to 70*? And just the same question for cooing the house, when the ground temp is stiil 58* and you get that pumped into the home you will quite certainly need it coolder then 58*, more likr 45-38- 30* might be needed. How do you cool the 58* that much lower?
    Please let me know your opinions on this as soon as you can, I’d appriciate it..Thanks

    • Keya Lea says:

      Using the relatively stable temperature a few feet underground, the temperature (58 degrees in your example) is collected from the ground, then into the building where there’s a heat pump.

      There are two main kinds of heat pumps: liquid to air and liquid to water heat pumps. Depending on setup and needs, a liquid-to-air heat pump (also called water-to-air) can output heated or cooled forced air into the building, or a liquid-to-water heat pump (also called water-to-water) which is a hydronic system, can use water to carry heating or cooling through the building for infloor heating or cooling.

  12. Daniel McVay says:

    I’m looking to build a new house and would like to have a underfloor heat and cooling system throughout the house. Would the underfloor system and a geothermal system work well together?

    • Keya Lea says:

      Hi Daniel,

      Actually, if you had a solar-based in floor heating system, you really wouldn’t need a geothermal system. Within a geothermal system, a lot of ground needs to be dug up to provide the stable, mean temperature. If you had a solar thermal heating system, you’d just need to have a floor with the tubing through it. Ideally, if you build a new your, why not build it passive solar? That way, it’ll be cool in the summer and warm in the winter.

      Best of luck to you!

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