Higher efficiencies through the process of condensing in furnaces
A condensing furnace is the technology that allows modern furnaces to achieve efficiencies above 90%. It works by forcing the hot exhaust gas created by the furnace’s burners through a specialized heat exchanger designed to increase the pressure on that hot gas to the point that it forces a change of state of the gaseous water present in the exhaust into a liquid.  When this change of state occurs, a large amount of energy is released in the form of heat.  So not only do you get the heat from the burning source fuel, you also get the heat from this chemical change of state.  The resulting liquid water that is created is drained out of the furnace.  The heat created is transferred over to the cooler air of your home and what you are left with is a combustion waste gas that gets expelled from the system.  Because of how efficient this condensing action is, the resulting combustion waste gas is so cool that it can be passed through plastic piping to the outside; this means you don’t need a traditional chimney.