Geothermal systems are great for replacement or retrofit applications. Most units are easy to install, particularly when they replace another forced-air system. They can be installed in areas unsuitable for fossil fuel furnaces because there is no combustion, thus no need to vent exhaust gases. Ductwork must be installed in homes that don't have an existing air distribution system. Another popular way to use geothermal technology is with in-floor radiant heating, in which hot water circulates through pipes under the floor to heat the room. Some companies offer tongue and groove subfloors that include the radiant floor piping in them for retrofit applications. G products are one of the most efficient, energy-saving, environmentally-friendly purchases you can make.