Here is my current situation described here with number crunching in detail. http://www.geoexchange.org/forum/ge...geothermal-addition-two-parts-due-length.html I do not trust the software I have really tried that estimates 1.5 tons for my first floor and 1.5 ton for the second floor because of the poor cold weather performace of my current 4 tons of cooling. The software does not take into acount that the second zone is over the first one. There is also not the option for R30 walls that are in my addition. I will have 3000sqft house located in central va with 1000sqft with R30 walls and R38+ attic. By the estimates in the software a 4 ton geo unit would be plenty. However, I currently have 2 2ton air source units and they could bairly keep up at below 20 outside with the current 1880 sft (actually closer to 2100sft since the builders finished the additional space for two walk in closets in the master bedroom which wasnt there before) without HVAC in the addition. I dont know if this was because of the cold air efficency loss described in the thread above or that I actually need 4 ton cooling for the current 1880 sft house. So I want to check my numbers before replacing my two air source pumps with one geo. I need to determine if replacing the second floor 2 ton with a geo 3 ton would be a better option and hopefully be able to come up with the cash for a geo 2 ton before 2016. IF anyone knows of any good free software or spreadsheets that would be appreciated. Thanks. I dont need anything too crazy because all the ceilings are 8 foot ceilings with standard insulation with exception of what I will do to the addition. Thanks as always.