Russ Root made an efficient move last year – to a new home he had built in Goshen, Conn. While it is considerably bigger than his former house, in Chenango Forks, N.Y., it will cost far less to cool and to heat. That is because he did something he had thought about ever since he built his last house, 15 years earlier: he installed a geothermal system instead of an oil-guzzling boiler. Now all the heat to warm his house is supplied by the earth beneath him. It’s pumped up, through plastic piping, in water circulating in his backyard six feet underground – where the temperature stays at about 45 degrees – and distributed by a fan through the house’s ductwork as air warmed to around 95 degrees. The bill for Mr. Root’s geothermal pump, its ground loop of piping and the house’s ductwork was just over $21,500. While a geothermal system, including labor, typically costs more than a comparable furnace and air-conditioning system, the price was about the same for Mr. Root, because the extra expense of digging and looping – $1,500 in his case – was more than offset by a $2,000 rebate from Connecticut Light […]