Are Geothermal Heat Pumps Overhyped and Overrated?

Now this is a real geothermal system, taking heat from steam in Iceland. This is not a heat pump. (Photo: Wikipedia).

What kind of heating system makes sense these days?

There is so much hype about geothermal heating and cooling systems these days; there is even talk of declaring Oct. 20 to be National Geothermal Day, “to raise awareness about environmental and economic benefits of geothermal energy and its vital role in building a clean and secure energy future.”

This is the first problem, because geothermal is the name for a really important renewable resource, the "the thermal energy contained in the rock and fluid (that fills the fractures and pores within the rock) in the earth's crust." There is a future for real geothermal in America, so the terms shouldn't be mixed up.

What they are really describing is what's known as a ground source heat pump or GSHP. Here is the definition of each:

  • Geothermal systems use heat directly from natural sources like hot springs, geysers and volcanic hot spots like the installation on the right in the Iceland photo above.
  • Ground source heat pumps are air conditioners that use soil or groundwater to cool the condenser instead of an outside coil and fan. It uses electricity to move heat energy from one place to another. Run it backwards and it provides heat, and more efficiently than using electricity directly.

The main problem with GSHP systems is that they are really expensive. All that drilling and piping costs a lot of money, and we are talking like $40,000 and sometimes $70,000, when in fact there are now significantly cheaper alternatives.

If you have a small and really well-insulated home, you can now get air to air heat pumps that can give you enough heat, even in Zone 6. Consultant Marc Rosenbaum has been using mini-split air source heat pumps almost exclusively. If you're willing to leave doors open in the daytime, you may not even need ductwork. He writes in Green Building Advisor:

Compact superinsulated homes in climates with design temperatures of 0°F or more can often be heated with a single zone unit with the wall cassette located in the main space. As long as the doors to other rooms remain open, the temperatures in those rooms will usually be within 2°F of the space where the cassette is located.

Certain units designed for cold climates can pull heat out of the air at down to minus 20 degrees F. So really, if you design your house properly in the first place, spending all that money on a GSHP system is a waste of money. You will save a lot more putting a fraction of the money into insulation.

fuel costs alternatives

What about gas?

Given that your ground source heat pump system is indirectly running on coal power, what about burning fossil fuels directly?

Using current fuel prices and the Energy Department Fuel Cost Comparison Calculator, (download spreadsheet here) I find that this year, my new high-efficiency gas boiler is actually cheaper to run than a ground source heat pump. Last winter, when gas supplies were low, it would have been a totally different story, but the point is, ground source heat pumps are overhyped.

If you live in the South and use air conditioning a lot, that's going to be a different set of calculations and it might make more sense. However the air to air units are getting better and better all the time and will give GSHPs a run for your money.

The single most important point in this discussion is that you cannot look at an HVAC system in isolation from the home where it is being installed. If you put money up front into design, siting and proper insulation, you don't have to pay a fortune for a GSHP. If you have an existing house, it may be more cost-effective to do a deep and extensive renovation than to drill all those holes or make all those trenches for the piping needed for a heat pump system.

Design it right in the first place and the ground source heat pump becomes expensive overkill.