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. (for more information, see here at the Geothermal Resources Council.)

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.
I've gotten myself into a lot of trouble criticizing GSHP systems in the past; a common response when I write is that I don't know what I'm talking about; this is my favorite: "If I were a geothermal contractor or manufacturer I would have asked that this be removed for falsely conveying what geothermal has to offer." That was seven years ago, and frankly the water has just got muddier since. There are so many myths and misconceptions about GSHP systems, many of which can be found on the National Geothermal Day page. These include:
Geothermal is a clean (no fossil fuel consumption) form of renewable energy that involves our sun heating the earth beneath our feet.
GSHPs are powered by electricity and in America, 46 percent of the electricity is generated by burning coal, a fossil fuel.
Through a geothermal system (geo for earth and thermal for the heat from the sun), we use that energy in the ground to heat and cool our homes.
When a GSHP is in heating mode, it is indeed extracting heat from the ground and that heat can be assumed to be from the sun, or from the natural heat from radioactive decay in the core of the planet. However in cooling mode, the GSHP is pumping heat into the already warm ground and there is zero gain of any kind from solar energy. In cooling mode it is nothing more than an air conditioner using the ground as a condenser. Do you think your AC unit runs on a renewable resource?
Geothermal is the most efficient form of heating and cooling that exists.
No it is not. That would be passive solar heating in a house with a lot of insulation and careful design.

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.

Previously in this series:

Lloyd Alter ( @lloydalter ) writes about smart (and dumb) tech with a side of design and a dash of boomer angst.

Are geothermal heat pumps overhyped and overrated?
Geothermal systems are hyped more than any other. Should they be?