Description Technical Documents Introduction AltSource, a combination of Boiler/Buffer Tank/and Optional Indirect Water Heater is the Air to Water Heat Pump or Geothermal Heat Pump's Best Friend. When Purchased with Indirect Copper Coil, AltSource allows for both space heating and ...Description Technical Documents Introduction AltSource, a combination of Boiler/Buffer Tank/and Optional Indirect Water Heater is the Air to Water Heat Pump or Geothermal Heat Pump's Best Friend. When Purchased with Indirect Copper Coil, AltSource allows for both space heating and domestic hot water preheating using the same energy efficient source of heat without the need of sophisticated control.