If land area is limited, closed loops can be inserted into vertical bore holes. Holes are drilled to a depth of about 250 to 450 feet. The U-shaped loops of pipe are inserted into the holes. The holes are then backfilled with a natural organic sealing solution. Each vertical pipe is then connected to a horizontal pipe, which is also concealed underground. The piping then carries fluid in a closed system to and from the geothermal unit. Vertical loops may be more expensive to install, but require less piping than horizontal loops because the earth, deeper down, is alternatingly cooler in summer and warmer in winter. If adequate land is available, horizontal loops can be installed. Using a chain trencher or backhoe, the loop installer digs one or more trenches three to six feet deep. A series of parallel piping is then laid in these trenches allowing fluid to run through the pipe in a closed system. Multiple layers of earth loop pipe can be laid in a trench with soil backfilled between the layers, but while this reduces the amount of land space needed, it may require more pipe. A typical horizontal loop will be 400 to 600 feet long per ton of heating and cooling capacity. Horizontal ground loops are easiest to install while a home is under construction, but new equipment allows loops to be installed under existing homes, buildings, or wooded lots with minimal disturbance to lawns. This special equipment bores holes horizontally under the surface and after about 250 to 300 feet of drilling, the pipe is inserted into the tunnel. If your home is near a pond or lake, this type of loop design may be the most economical because these loops often require less excavation than vertical and horizontal loops. Polyethylene piping is run to the water underground and then long sections are submerged under water. The pipe may be coiled in a slinky shape to fit more of it into a given amount of space. The fluid then circulates through the piping, just as it does in ground loops, to the geothermal unit. Typically, a 1/2 acre, 8-foot-deep pond or lake is usually required to assure sufficient heat-transfer capability.