I installed a geothermal system when I built my house in 1995 at a cost that was fairly close to the same as the most efficient furnace/air conditioner at the time. I'm rural so I avoided the swings in price of LP over the years. Recovery times do not make setback thermostats very practical so we set ours to 71-72 and leave it be. Biggest drawback is loss of electrical service but even in a rural setting those events have been few and far between.In general, you lower your heating bill by 3% for every degree you turn down your thermostat.
