This seems like a good example of a technical efficiency that needs a corresponding legal and transactional efficiency to go with it. Assuming that a ground source system involves mutiple parcels of private property, each with a bank loan, the social cooperation here would legally take the form of a cross easement and maintenance agreement among each property owner. The agreement would be of record, grant appropriate property rights to each property owner, run with the land (i.e., be permanent) and provide for the common maintenance, repair, and replacement of the system. Because of provisions typical to most loan documents, lender approval of the easement and maintenance agreement would probably be required. Thus, if each property owner has to hire an attorney to knock the agreement out and get lender approval for it, the transaction cost and legal issues may become an issue or barrier to getting things done. Legally, it would be easier to do this for multi-family housing, whether owned by a single entity or put into the condominium form of ownership, because the developer can just make it so. Well systems placed within public rights of way and connecting to private property would probably require a law change. My ultimate point in noting the above is that our laws should serve the identified efficiency needs and not stand in their way. And, in a gross simplification, our property laws particularly tend not to provide for or consider more modern and necessary values such as cooperation, conservation and preservation. Thus, I agree with the point about cooperation and note, in addition, that our laws and legal system should adapt to further it.

I probably should have made clear. That 10,000 was in an apartment complex - with multiple units per building. I doubt that heat pumps, even shared for single family homes will get that cheap. But along both sides of a street for a block we might get to $15,000 per residence. The tradeoff in sharing comes when the cost of additional piping to move  heat long distances exceeds the savings from various economises of scale.  Sunflower at one point was claiming that even at neighborhood level, square miles, district pay offs compared to smaller units. Don't know if he still thinks that. It looks to me like for single family homes the optimum occurs at a much lower scale, though for apartments and densely populated urban areas where residents mostly live in multi-unit buildings he could be right. At any rate I think that for single family homes we will end up at $15,000 per unit or close to that, and that for apartments and multi-unit buildings that are a couple of stories or so we probably can come closer to $10,000 per unit. Where you have hundreds of units per building the cost may be even lower. On the other hand in skyscraper and mid-scrapers (anything much above five stories) you run into other problems - the need to dig boreholes, cause there is not way to serve than kind of building with broad shallow loops (unless they have really big parking lots). And I believe modifying ducting in tall buildings is a major pain. I wonder if a green builder reading this can describe the problems and potential for tall buildings, how they differ from short buildings, and how they are similar.

Hal9000, this indicates that governments need to be more involved in this process -- and I know this sounds pie-in-the-sky, but if local governments at least built up much of the infrastructure (piping?), then the legal issues would fade.

If ground source heat pumps are cheaper per person for apartments, then I just want to point out that that's another benefit of apartment buildings, in addition to the lower heating costs because of the lower roof per household area, and because of the density advantages.  But I know, America wants single family homes.