maintain a constant pressure in the ventilation system, then the reduced pressure drop leads to a slowing of the fan motor and thus reducing power consumption, and in turn improves the seasonal efficiency of the system. Use in metallurgical furnaces Recuperators have also been used to recover heat from waste gasses to preheat combustion air and fuel for many years by metallic recuperators to reduce energy costs and carbon footprint of operation. Compared to alternatives such as regenerative furnaces, initial costs are lesser, there are no valves to be switching back and forth, there are no induced-draft fans and it does not require a web of gas ducts spread up all over the furnace. Historically the recovery ratios of recuperators compared to regenerative burners were low. However, recent improvements to technology have allowed recuperators to recover 70-80% of the waste heat and pre-heated air up to is now possible. Gas turbines Recuperators can be used to increase the efficiency of gas turbines for power generation, provided the exhaust gas is hotter than the compressor outlet temperature. The exhaust heat from the turbine is used to pre-heat the air from the compressor before further heating in the combustor, reducing the fuel input required. The larger the temperature difference between turbine out and compressor out, the greater the benefit from the recuperator. Therefore, microturbines (<1 MW), which typically have low pressure ratios, have the most to gain from the use of a recuperator. In practice, a doubling of efficiency is possible through the use of a recuperator. The major practical challenge for a recuperator in microturbine applications is coping with the exhaust gas temperature, which can exceed . Other types of gas-to-gas heat exchangers Heat pipe Run-around coil Thermal wheel, or rotary heat exchanger (including enthalpy wheel and desiccant wheel) Convection recuperator Radiation recuperator See also Air handler Energy recovery ventilation Heat recovery ventilation HVAC (heating, ventilation, and air conditioning) Indoor air quality Regenerative heat exchanger Thermal comfort References External links Energy conservation Energy recovery Engineering thermodynamics Heat exchangers Heat transfer Heating, ventilation, and air conditioning Heating Industrial equipment Low-energy building Mechanical engineering Sustainable building