Illustration of a geothermal heating and cooling system that handles multiple loads for a community. Illustration by Sarah Cheney.

Illustration of a geothermal heating and cooling system that handles multiple loads for a community. Illustration by Sarah Cheney.

Imagine a home in which the temperature is always comfortable, yet the heating and cooling system is out of sight. That system performs efficiently but doesn’t require extensive maintenance or knowledge on the part of the owners.

The air smells fresh; you can hear the birds chirping and the wind rustling lazily through the trees. The home shares energy with the earth similar to the way the roots of the trees exchange the essentials of life to their leaves and branches. Sounds comfortable, doesn’t it?

Geothermal heating and cooling makes that vision a reality. Geothermal HVAC (heating, ventilating, and air conditioning) brings a building in harmony with the earth beneath, taking advantage of subterranean temperatures to provide heating in the winter and cooling in the summer.

How Geothermal Heating and Cooling Works

Outdoor temperatures fluctuate with the changing seasons but underground temperatures don’t change as dramatically, thanks to the insulating properties of the earth. Four to six feet below ground, temperatures remain relatively constant year-round. A geothermal system, which typically consists of an indoor handling unit and a buried system of pipes, called an earth loop, and/or a pump to reinjection well, capitalizes on these constant temperatures to provide “free” energy.

(Note that geothermal HVAC should not be confused with “geothermal energy,” the process by which electricity is generated directly from the heat inside the earth. That takes place on the scale of utilities and uses different processes, normally by heating water to boiling.)

The pipes that make up an earth loop are usually made of polyethylene and can be buried under the ground horizontally or vertically, depending on the characteristics of the site. If an aquifer is available, engineers may prefer to design an “open loop” system, in which a well is drilled into the underground water. Water is pumped up, run past a heat exchanger, and then the water is returned to the same aquifer, through “reinjection.”

Diagram of how geothermal HVAC systems work

Diagram of how geothermal HVAC systems work. Illustration from Modern Geothermal HVAC

In winter, fluid circulating through the system’s earth loop or well absorbs stored heat from the ground and carries it indoors. The indoor unit compresses the heat to a higher temperature and distributes it throughout the building, as if it were an air conditioner running in reverse. In summer, the geothermal HVAC system pulls heat from the building and carries it through the earth loop/pump to reinjection well, where it deposits the heat into the cooler earth/aquifer.

Unlike ordinary heating and cooling systems, geothermal HVAC systems do not burn fossil fuel to generate heat; they simply transfer heat to and from the earth. Typically, electric power is used only to operate the unit’s fan, compressor, and pump.

A geothermal cooling and heating system has three main components: the heat-pump unit, the liquid heat-exchange medium (open or closed loop), and the air-delivery system (ductwork) and/or the radiant heating (in the floor or elsewhere).

Geothermal heat pumps, as well as all other types of heat pumps, have efficiencies rated according to their coefficient of performance, or COP. It’s a scientific way of determining how much energy the system moves versus how much it uses. Most geothermal heat pump systems have COPs of 3.0 to 5.0. This means for every unit of energy used to power the system, three to five units are supplied as heat.

Geothermal systems require little maintenance. When installed properly, which is critical, the buried loop can last for generations. The unit’s fan, compressor, and pump are housed indoors, protected from the harsh weather conditions, so they tend to last for many years, often decades. Usually, periodic checks and filter changes and annual coil cleaning are the only required maintenance.

Geothermal HVAC Spreads

Geothermal HVAC systems have been used for more than 60 years in the U.S. and beyond.

They work with nature, not against it, and they emit no greenhouse gases. (As mentioned earlier, they use a smaller amount of electricity to run, because they are coupled in with the earth’s average temperature.)

Geothermal HVAC systems are becoming common features of eco-friendly homes as part of the growing green building movement. Green projects accounted for 20 percent of all newly built homes in the U.S. last year. By 2016, a Wall Street Journal article predicted that green housing will grow from $36 billion a year to as much as $114 billion. That’s approaching 30 to 40 percent of the entire housing market.

But a lot of information out there on geothermal heating and cooling is based on outdated information, or outright myths. In our new book Modern Geothermal HVAC Engineering and Control Applications (Egg/Cunniff/Orio -McGraw-Hill 2013), co-authors Greg Cunniff, Carl Orio and I bust many of these myths.

Geothermal HVAC Myths Busted

1.     Geothermal HVAC systems are not considered a renewable technology because they use electricity.

Fact: Geothermal HVAC systems use only one unit of electricity to move up to five units of cooling or heating from the earth to a building.

2.     Photovoltaic and wind power are more favorable renewable technologies when compared to geothermal HVAC systems.

Fact: Geothermal HVAC systems remove four times more kilowatt-hours of consumption from the electrical grid per dollar spent than photovoltaic and wind power add to the electrical grid. Those other technologies can certainly play an important role, but geothermal HVAC is often the most cost effective way to reduce environmental impact of conditioning spaces.

3.     Geothermal HVAC needs lots of yard or real estate in which to place the polyethylene piping earth loops.

Fact: Depending on the characteristics of the site, the earth loop may be buried vertically, meaning little above-ground surface is needed. Or, if there is an available aquifer that can be tapped into, only a few square feet of real estate are needed. Remember, the water is returned to the aquifer whence it came after passing over a heat exchanger, so it is not “used” or otherwise negatively impacted.

4.     Geothermal HVAC heat pumps are noisy.

Fact: The systems run very quiet and there is no equipment outside to bother neighbors.

A technician inspects a geothermal HVAC air handler

A technician inspects a geothermal HVAC air handler. Photo courtesy of Jay Egg

5.     Geothermal systems eventually “wear out.”

Fact: Earth loops can last for generations. The heat-exchange equipment typically lasts decades, since it is protected indoors. When it does need to be replaced, the expense is much less than putting in an entire new geothermal system, since the loop or well is the most pricey to install. New technical guidelines eliminate the issue of thermal retention in the ground, so heat can be exchanged with it indefinitely. In the past, some improperly sized systems did overheat or overcool the ground over time, to the point that the system no longer had enough of a temperature gradient to function.

6.     Geothermal HVAC systems only work in heating mode.

Fact: They work just as effectively in cooling and can be engineered to require no additional backup heat source if desired, although some customers decide that it is more cost effective to have a small backup system for just the coldest days if it means their loop can be smaller.

7.     Geothermal HVAC systems cannot heat water, a pool, and a home at the same time. Fact: Systems can be designed to handle multiple loads simultaneously.

8.     Geothermal HVAC systems put refrigerant lines into the ground.

Fact: Most systems use only water in the loops or lines.

9.     Geothermal HVAC systems use lots of water.

Fact: Geothermal systems actually consume no water. If an aquifer is used to exchange heat with the earth, all the water is returned to that same aquifer. In the past, there were some “pump and dump” operations that wasted the water after passing over the heat exchanger, but those are exceedingly rare now. When applied commercially, geothermal HVAC systems actually eliminate millions of gallons of water that would otherwise have been evaporated in cooling towers in traditional systems.

10.  Geothermal HVAC technology is not financially feasible without federal and local tax incentives.

Fact: Federal and local incentives typically amount to between 30 and 60 percent of total geothermal system cost, which can often make the initial price of a system competitive with conventional equipment. Standard air-source HVAC systems cost around $3,000 per ton of heating or cooling capacity, during new construction (homes usually use between one and five tons). Geothermal HVAC systems start at about $5,000 per ton, and can go as high as $8,000 or $9,000 per ton. However, new installation practices are reducing costs, to the point where the price is getting closer to conventional systems under the right conditions.

Factors that help reduce cost include economies of scale for community, commercial, or even large residential applications and increasing competition for geothermal equipment (especially from major brands like Bosch, Carrier, and Trane). Open loops, using a pump and reinjection well, are cheaper to install than closed loops.

Thanks for the thousands of likes and hundreds of comments!  National Geographic has closed comments for this blog.  Please continue the conversation and get the answers you need for geothermal heating and cooling on Jay Egg’s blog, “Geothermal Heating and cooling Questions and Answers

Jay Egg is the co-author of the new book Modern Geothermal HVAC Engineering and Control Applications (McGraw-Hill 2013), with Greg Cunniff and Carl Orio. He co-wrote the book Geothermal HVAC, Green Heating and Cooling in 2010 with National Geographic’s Brian Clark Howard. Jay consults with the geothermal HVAC industry. He previously served as an installer of the technology through his company EggGeothermal.


  1. Linda Moore
    NE, OK
    June 5, 2015, 7:50 pm

    Hello, our HVAC unit is getting pretty old and we have a friend that recommends using Geothermal. We are in a 2 story house, that currently has 2 hvac zones and is on a slab. We also have an existing pool. Can you tell me, would we be able to add a system to this house? Have zones? and can the pool be used as the ground source/aquifer? Thanks!

  2. Jay Egg
    May 28, 2015, 7:35 am

    Abhijit in Mumbai,
    The average temperature of shallow groundwater in Mumbai is 25C-27C (~77F-80F). Because the mean maximum average temperatures is about 32C (90F) in summer (about 5-7C higher), the efficiency of a ground water cooled (geothermal) heat pump is superior to any other type of cooling.
    Please let me know your progress with regard to installation of a geothermal heat pump. I’d like to hear how it goes for you!

  3. Jay Egg
    May 19, 2015, 8:34 am

    Georgia in Missouri,
    Thank you for your query. I am grateful you have come to this forum to research your options.
    The leak in your coil is the exception and not the rule by a wide margin, as most geothermal heat pumps last 25 years+ with no major issues. I recommend you seek guidance from a professional from the IGSHPA provider website . It may be best to have 3 different providers give you recommendations before you make your choice.
    The loop installation you have described is different than normal practice. This is something that you should bring up to the providers that you bring out to evaluate the system for upgrade/replacement. I would like to hear from you after you have your options presented.

  4. Abhijit Patil
    May 19, 2015, 6:23 am

    What is the temperature of water in borewell in degree celcius?

  5. Georgia
    May 14, 2015, 3:43 pm

    Our geothermal unit has been repaired many times and now the coil it leaking after only 8 years. It only operates on the back emergency heat. We are considering replacing the geothermal but an issue has been raised about the ground loops. We believe they are in one trench and they may be stacked instead of side by side. Either way the are in one trench that may be 2 to 3 feet wide. Is this a good way for the loops to be placed. If we replace only the unit inside would the way the loops are placed effect the efficiency of our system?

  6. Jay Egg
    May 1, 2015, 6:25 am

    Wallace in BC,
    The exchanger/copper should last for 20 years or significantly longer. I’ve found that there are three items that can damage an exchanger in the manner you have described: 1-Electrolysis, 2-Corrosives in the water/fluid, and 3- improper flow rates. Each of these is addressed in chapters 6 and 7 of “Modern Geothermal HVAC Engineering…” . One of the lesser known causes of premature water coil failure, electrolysis, is also often the culprit. I will just say that the importance of grounding the system extraordinarily well can’t be overstated. I highly recommend reading chapter 6 of the aforementioned text, and it will enlighten you as it did me. The need of a flow restrictor is also imperative. The GHP’s are designed for a certain flow rate, and more or less flow causes various issues, the same as it would in any mechanical device. Take the time to identify a good geothermal professional to engage in this process if you do not already have one. The European Ground Source Heat Pump Association (EGSHPA) is a great resource for professionals there .
    Please take the time to update me on your progress; I’m here to help!

  7. Jay Egg
    May 1, 2015, 6:22 am

    Murray in BC,
    Thank you for taking the time to share this issue with me. As with most problems of this nature, there is something in the system that is using more energy than it should be using. The problem is not likely with the geothermal heat pump. If I were to guess based on my experience, I would suggest looking at the pumping energy (the pump that moves the water through the system). In Chapter 5 of the book, “Modern Geothermal HVAC Engineering…” , it is stated on page 151 that, “…most [pumps] are significantly over-sized…due to errors or omissions…] . This can significantly increase energy consumption. I recommend that you have a qualified geothermal professional take a look at what is using the additional power.
    Please let me know what you find out; I want to know!

  8. Murray Banting
    Nanoose Bay, BC
    April 28, 2015, 1:56 am

    We have an ocean loop geothermal system and it works well but expensive on electricity, no savings in fact likely more than conventional. We only heat no cooling but our home uses as much electricity for just the heat and fridges as other homes in our area use for the whole household. We were recently away for two weeks and the graph we can see on our electric consumption from BC Hydro shows our house using just fridges and heat was equal to 45 kwh pr day. When we are all home (4 of us) we average 95 kwh per day so it doubles when we are home. Our home is 4500 sq.ft newly built in temperate pacific NW. Its very pricey to put in and pricey to use is my conclusion.

  9. Wallace Mah
    Agassiz, BC
    April 12, 2015, 1:10 pm


    Is it normal for the copper water coil to wear out so soon on the geothermal system that is only seven years old. I am a bit perplexed after doing more research on geothermal systems as I understand they are suppose to be more efficient, and the system should last for decades. Our system which is both external and internal has been problematic from day one. It has froze up a few times which requires thawing out, and dispenses additional water from the overflow box. Our system uses water and refrigeration fluid (freon) as well. In my research we discovered that we did not have a water flow restrictor and the company is now saying that we should add that in for 250.00 Is it possible that without the water flow sensor restrictor that it damaged the copper water coil?
    Thanks Wallace

  10. Jay Egg
    April 11, 2015, 2:31 pm

    Joe in Tampa,
    Many have asked the same question as you are asking, especially when you consider that ground temperatures in Florida are nice and cool in the lower to mid 70’s year round. But heat transfer just does not take place effectively at such a small difference in temperature (we call that a “Delta T”). The fact is, to have reasonably effective heat transfer we need a 30F Delta T. This does two things for you: (1) It provides humidity removal as water vapor condenses on the indoor air coil, runs down into the condensate pan and drains out of the space, and (2) It produces an air delivery temperature of about 55F to 60F, which is the temperature that is required to give the cooling effect we need when it’s hot (and humid) outside. The geothermal heat pump (GHP) works with those cooler temperatures underground to give you that premium efficiency only attained with a GHP. That’s easy to understand when you consider that other “air-sourced” heat pumps are still fighting with much higher outdoor temperatures.
    The real plus to all of this is that the refrigeration system required to do this magic of manipulating temperatures also has a byproduct we can really use; waste heat. In a standard AC system, this would be exhausted to the outdoor air through the condenser fan (on the outdoor unit). But on a GHP, you can get a “Hot Water Generator” feature that put all that heat into the domestic hot water (DHW) tank, providing most of the hot water you need for showers, laundry, etc. Here’s a little primer:
    I hope this helped out!