A local installer said that if water is always at the top of a vertical column, then grout is not needed and that grout reduces performance. However, I read that grout is used to prevent contamination of aquifer. And that thermal grout has twice the thermal conductivity as water (1-1.2 vs 0.58). The latter seems surprising, given water's capacity to store heat. Any thoughts? Has anyone ever seen or heard of an ungrouted vertical loop? Perhaps shared with a well (but pump replacement would be a pain)? This topic raises interesting questions: http://www.geoexchange.org/forum/ge...silica-sand-and-thermally-enhanced-grout.html This quote in particular "It is important to note hear that .88 is double the standard of around .40-45". Does this mean that non-enhanced grouts are this low number - which is well below water? In theme of my header spacing thread (2' vs 50'), given the slow rate of heat transfer in the ground, is thermal grouting a bit over touted? http://www.geoexchange.org/forum/ve...ops/5207-pipe-spacing-from-vertical-loop.html Lastly, was told shale is excellent for geothermal. Yet according to charts found, it is among the poorest. For example: http://www.gly.uga.edu/railsback/PGSG/ThermalCond&Geothermal01.pdf These 'doubts' are a concern that being told 150' vertical bore / ton is good ... now sounds like in would be inadequate.