Geothermal
"Geothermal" is heating with underground hot water. This is very rare, and usually requires very deep drilling, except in a few areas where there is hot water near the surface.
Ground Source Heat Pump (GSHP)
However, in many areas, you can drill down into the ground and take heat away in the winter, and supply heat back into the ground in the summer, using a "ground source heat pump" system. Or, sometimes horizontal trenches are dug and pipe is laid in them for the heat sink. Or, sometimes a lake or the sea can be used - you arrange some coils of plastic pipe in the water, and do the same thing.
Cost
The cost is the key. Find out if the heat transfer characteristics are correct from a proper well-driller-installer of ground source heat pumps. If your area is OK for this, then go for it. There is a capital cost, and you have to decide if you like the idea and the long pay back.
If you decide to go ahead, then you need, a well(s), a pump system for the water, a heat pump, a buffer tank (usually), a peaking water heater (usually - an economic decision), then an air distribution or water distribution system.
Pictures
Here some pictures of a large social housing project that I worked on in Vancouver, BC, Canada.
Geothermal ground source heat pump housing
Particularly interesting in the "slide show" are some unique small fan coil units that successfully operate. These are Canadian made and work well. These units will cool and heat. You can use a more common air distribution system for heating and cooling, or a common in-floor radiant for heating only - still all of these use the other basic heat pump equipment and ideas in the slide show for this project.
Boring (not for me) Calculations
The "heat transfer"
Heat transfer calculations information I talked above are some of the terms shown in the typical calculations on this link. Your local supplier should make these calculations and you should ask for a copy to review.
Local Installer
There are installers who specialize in most areas in small (and larger) single family residential ground source heat pump systems and can help you figure out the cost and pay back. Or understand the cost connected with your desire to help use less electrical power and/or be more energy efficient.
I think using a GSHP is a good idea, and heat can usually be had for about 1/4 of the cost of electrical power (depending on several things).
Zero Energy Use
The idea of having zero net energy use is greatly helped by highly efficient system like these GSHP systems. Once we get our energy use very low, then with solar voltaic power generation (and other renewable ideas) we can have at least a zero-connected-to-the-grid-energy-use-house. The cost is more, maybe $18,000 for a big house, and the pay back is real long. I am not talking about not being connected to the grid - use the grid - just don't use ANY energy that you do not generate.
And, what about a granite counter top - every new place in Vancouver and San Diego HAS to have those tops. They are not "cost effective" - people pay a lot extra for them because they want them or MUST have them. What's the difference with just having to have a "net-zero-energy-use" house.
Vision
Most of us can live with zero energy use. Are we strong enough to do it? Will we pay for it? Even if it cost more than not doing it. Wouldn't it be great to live with zero net energy use, day in and day out, every day, everyone?
OK, OK, almost everyone.
Alex