This seems pretty nice Only thing i have found of it too. lot easier than digging hundreds of feet flat 8 ft deep. My only wonder is . How the heck does the guy keep out the rain water from his hole. The hole in rainy season would fill up with ground water. unless it was closed somehow but that seems like that would make it even more less efficient. And obviously the guy needs to space these things out a good bit. He is basically getting all his useable heat from the ground spacing them less than 2 feet apart ground doesnt give up heat quickly