I just bought two of these: http://www.bosch-climate.us/products-bosch-thermotechnology/geothermal-heat-pumps/geothermal-residential-product-offering/water-to-

I just bought two of these: http://www.bosch-climate.us/products-bosch-thermotechnology/geothermal-heat-pumps/geothermal-residential-product-offering/water-to-air-geothermal-heat-pump-systems/greensource.html http://www.bosch-climate.us/products-bosch-thermotechnology/... I have only installed one, and I can't comment on how effective it is at reducing cooling costs as it's a new home (though I lived there for a couple of weeks before I got the heat pump units). But I can comment on the "why not". Generally it's very expensive to install because it requires several thousand feet of underground pipe to normalize the temperature of the water going through the system. Many homes don't really have enough land to support this horizontally. You can install the loop vertically (like a drilled well), which is again, pretty expensive up front. Few take the long view. I happen to have plenty of land and a backhoe so I just dug a ditch.