Geothermal Heating Systems for Homes

Domestic Geothermal heating systems can be a great way to heat a home, replace a furnace, and are labeled as money savers. Question is, are they worth the hype? Here's a quick view first of how they operate.

Starting at depths of between 6 and 10 metres, the temperature of the earth is no longer influenced by variations in surface temperature, and stays relatively constant at around 8 to 10 C. So the underlying principle of geothermal heating and cooling is to use that consistent interior earth temperature to balance our wildly varying North American & Canadian surface temperatures.

With the use of heat pumps, geothermal heating and cooling systems extract heat energy and transfer it into buildings, saving approximately 50 to 60% on heating and cooling costs, depending on the fuel being compared to.

In summer months, geothermal cooling functions in a similar way to standard air conditioning, only heat is not simply ejected into the outside air, but rather deposited deep in the ground for future use. The result is guilt-free air conditioning because the heat extracted in summer months is actually used to warm the earth deep below, heat which will increase the efficiency of the ground source heat pump in winter months.

Geothermal home heating systems:

Vertical closed-loop geothermal systems have a sealed U-shaped pipe of high density polyethylene that carries a heat transfer fluid (usually a water / methanol mix) in a continuously circulating loop allowing an exchange of heat by conduction. As the liquid returns to the surface, either heated or cooled depending on the season, the additional or reduced amount of heat in the water is used to condition the home. The required depth for this system is generally 300 feet or more, and the cost is calculated by the foot. Through the nose, but by the foot.

Geothermal vertical loop system © Alexandre Gilbert

Horizontal closed-loop geothermal systems function in the same manner as vertical systems, except that pipes are run back and forth 6 to 10 feet underground. Installation involves excavating trenches (at least 300 feet of them), rather than digging a well.

Horizontal ground source heat pump systems can be cheaper to install but require a significant amount of space, and it does some pretty intense damage to any ecosystems that lay in its intended path. For a given length of pipe, horizontal loop systems are a bit less efficient than vertical loop systems, as they can be more easily affected by surface temperatures. The other downside is that if or when there's a leak in the circuit, with a horizontal mat or grid style system the whole garden area has to be dug up again in search of a tiny leak that is losing the system pressure.

Geothermal horizontal loop system © Alexandre Gilbert

Open-loop geothermal systems use ground water pumped directly from a supply well (75 to 100 feet deep) in order to draw and inject heat. Water is pumped out of the first well, and after the heat exchange is carried out, it gets injected into the second well.

Geothermal open loop system © Alexandre Gilbert

Open-loop systems have a very high thermal efficiency and installation can be up to 50% less expensive than vertical closed loop systems. However, conditions necessary for the proper function of these systems are rarely found in urban areas, as they require an abundant source of ground water and a high water table.

Will geothermal heating save me money?

That truly depends on the size of the project to heat. No geothermal system is cheap to install, and because it offers only a reduction in consumption, the return on investment is really only viable for larger buildings. For this reason geothermal is more suited to commercial or multi-unit residential projects of substantial size.

A home would have to be quite large, and somewhat poorly-insulated to actually make it pay for itself in a reasonable time frame. In many cases, particularly with moderately-sized new homes being built, that large of a financial investment towards energy efficiency could offer much greater returns if put towards heat retention instead - better windows, additional home insulation in new build, insulating existing walls from the outside during a house renovation, or better tapes and membranes for air sealing, etc. 

Ball park pricing for a geothermal system: For an averaged size home (2000 sq. ft.) a GSHP will easily cost $30,000 to have installed, and that is in exchange for a monthly saving of about 50% on the heating bill. So payback for the average single family home is simply too far away to make this a financially competitive option with all but the highest consuming homes - and even then only when the boiler or furnace has failed and needs replacement. 

That same investment of $25,000 (or perhaps less) in a better thermal envelope would likely reduce heating bills easily by 70 or 80%, perhaps more. Geothermal energy is an excellent global technology, but poorly insulated single family homes will get far more bang for the buck if the money is put into insulation instead, or balanced between energy saving renovations and high efficiency heat pumps.

Now you know more about Geothermal heating for homes, learn more about sustainable home comfort, energy efficiency and how to reduce the carbon footprint of homes on the following pages and in the EcoHome Green Building Guide pages.

Find more about green home construction and reap the benefits of a free Ecohome Network Membership here.