When you calculated savings did you also count in savings from the de-superheater as well? With our city water coming in at 52 right now that can really add up.

As has been mentioned the cost of a standalone AC might be $2-$4K, so you could also take that off the cost of the system, if you want to look at it that way.

Are you planning on going with time of use electric rates? That can cut your geothermal electric bill and system payback almost in half. You do then have to live with on peak off peak and some temperature swings, for instance setting you thermostat for 70F off peak and 60-65F on peak. If you do this you have to disable the aux heat on most systems so it won’t kick in when off peak hits. But if you do plan on time of use rates let the HVAC guys know as they will have to increase the size to account for only being able to heat 14 of the 24 hours. Initially I found it odd the field size doesn’t change just the pump size since your taking the same BTU’s out of the field in 24 hours, just in a shorter time to move them. Or if you go with a “hybrid” system that can use geo or gas you can set the gas to be used on peak and geo off peak, ours is setup this way.

And as Craig mentioned don’t forget to include the monthly fees for being connected to gas. For 9 months of the year we use 0-1 therms a month (gas range and fireplace) paying about $1 a therm, but paying almost $12 a month just to be connected. If I had to do it again I would have gone with propane and a good wood burning fireplace, even with a good gas fireplace I can’t stand to see the fireplace on knowing it’s only about 80% efficient.