What is geothermal heating?

Geothermal heating is a system using the heat from underground sources to heat domestic homes and industrial plants. There are three types; ground source heating, direct use geothermal and deep geothermal. 

Ground source heating is where a ground source heat pump circulates liquid that has absorbed heat from underground through a network of pipes and the heated liquid is passed through a heat exchanger to heat or cool the house. 

Direct use geothermal and deep geothermal systems use groundwater and steam from underground (deep underground in the case of deep geothermal systems). They can only be used in certain areas of the world where there is volcanic or tectonic activity. 

Geothermal heating with a ground source heat pump

Geothermal heating with a ground source heat pump is a good clean way to heat (or cool) your home. A small amount of electricity is needed to drive the ground source heat pump. If that electricity is supplied by renewables, like solar energy or wind power, the whole geothermal heating system can be renewable. 

The temperature of the ground, even very close to the surface, is constant year round (United States Environmental Protection Agency). Whether it is winter or summer, and no matter how hot or cold the ambient temperature, this constant temperature means that a ground source heat pump can circulate warmer or colder air, as necessary, into your home.

What is a ground source heat pump?

A ground source heat pump sits on the surface of the ground. It circulates liquid, or geothermal fluid, through a system of pipes (Energy Saving Trust). It sends the cooled fluid out to absorb ground temperature heat, then brings it back into the house. 

It transfers the now heated fluid to a refrigerant which compresses the liquid to increase the heat, then passes it via a heat exchanger which heats the water in the house in radiators, underfloor heating or in the water tank. The system can also be used to cool a house. 

What is geothermal fluid and is it safe?

Geothermal fluid is the liquid that is pumped around the geothermal heating system by the ground source heat pump. The fluid is a mix of water, antifreeze and refrigerant or just refrigerant. 

The waterless version uses R-410A refrigerant, the same as in your domestic fridge. It has been approved by the EPA as safe and environmentally friendly to the earth. The conventional mix including antifreeze is harmful to groundwater. 

Closed loop and open loop geothermal heating systems

An open loop system uses two boreholes. One that extracts groundwater which is already close to the temperature of the ground around it. It circulates the water and then returns it back to the ground through the second borehole. Some regions require treatment of the water before it is released.

Closed loop systems are the most common with four different types: horizontal loops, vertical loops, slinky systems and pond loops. 

Pond loops are simply looped into water nearby. This means no digging, but the water needs to be deep enough so that the loops are not affected by surface temperatures.

A geothermal heating system with horizontal loops will require trenches of 100-400 foot in length. The loops also have to be a certain distance apart. 

The ‘slinky’ method of looping the pipes saves some space (Office for Energy Efficiency & Renewable Energy). Pipes are coiled and placed at two heights or side by side in a trench.

Vertical boreholes can be anywhere from 150-400 foot deep and 20 feet apart. The temperature at these deeper ranges is more constant and therefore more efficient. 

Vertical loop systems are around 10% more efficient than horizontal loop systems, says Great Lakes Geothermal and they take up less space. That said, the initial install cost of a borehole for vertical loops is higher than digging in horizontal loops (depending on the soil type). 

Either way, the cost of installing the pipes for a geothermal heating system is one of the highest costs of the project. 

Geothermal heating cost

The geothermal heating cost for an average American home is between $10,000 and $30,000 (Undecided with Matt Ferrell). 

This varies depending on the type of system you install from $9,000 – $15,000 for an open loop system, $12,000 – $25,000 for a horizontal closed loop system to $15,000 – $30,000 for a vertical closed loop system. Compare this to installing a traditional HVAC system which is between $7,000 and $12,000 all in. 

If these install costs have put you off, don’t forget to look into tax incentives that can reduce that amount by 30% or more. Then reckon the savings over a conventional HVAC system of around $600-$1400 per year. 

The payback on geothermal heating sits between eight and ten years. The heat pumps are likely to last twenty years or more, and the ground infrastructure for fifty years or more. 

These figures are compelling, even without the gain of making your home more sustainable

Is geothermal heating worth it?

Based on the figures we have included, geothermal heating is worth installing if you can afford the initial high installation costs. The long term benefits of a geothermal heating system are reducing energy bills, low maintenance, and an early payback. 

In addition, geothermal heating will not only save money but also be better for the environment. If you use clean electricity to run the ground source heat pump, installing geothermal heating will eliminate any dependency on fossil fuels.