The same ducts used by the air-conditioner in summer distribute hot air in winter. That means no oil deliveries, no boilers, no noisy outdoor condensers and no pollution. The expensive part is drilling to put in ground loops. The loops are filled with water or water mixed with a nontoxic antifreeze. The longer the loop, the more heat it can gather from the earth.
People think Manhattan is inhospitable to geothermal energy because it is built on bedrock.
But granite is excellent for transferring heat. The gravel and sand of Brooklyn and Queens are even better. Cost efficiency dwindles with increasing size. The geothermal payback can take at least three years. Some utility companies provide grants or rebates to encourage homeowners to go geothermal.