Geothermal is a pretty big commitment in terms of upfront cost. You still need electrical power to run the heat exchangers, fan and pump...I assume you are talking about products like Waterfurnace? Another thing necessary is a large enough lot for the horizontal pipes...in an area where you won't be digging ever again. That said, if you can put out the initial cash, the heat is pretty much free for the rest of your life. Combined with a solar array, you are not paying anything for heat, ever again. I'm not familiar with dual fuel furnaces.

Thank you for taking time to respond. Good things to consider.