I am getting quotes for a geothermal retrofit in Lancaster PA (just West of Philadelphia) and am considering various options. One contractor gave me a choice of either a 2 ton or 3 ton (2-stage), saying that the 3 ton would provide essentially all my heating, the 2 ton would need some auxiliary. Another contractor only suggested a 3-ton system. I'd like to beef up my passive heating and insulation, perhaps even add a fireplace insert for really cold days, and get the 2 ton. In this way I'd be very efficient in the summer and reduce some load overall. But I'm a little worried I'll be burning a ton of firewood or using a lot of auxiliary - offsetting the whole point of going geothermal.

I currently have an airsource heat pump that seems to be good for only about 30% of the really cold winter months (Dec - Feb), propane kicks in otherwise. I will get rid of the propane backup with the new setup.

My question is this: how much better will the 2 ton geothermal be compared to a 10 year old air source heat pump? If I do much better with it, will the 3 ton be overkill? Is it better to be a little light on heating load ... or the converse for colder climates?

Thanks for any thoughts.