An indirect system is a heating system where the heat emitters are not in direct connection with a boiler or district heating system. The separation takes place by placing a heat exchanger in the heating system.
IEC efficiency standard
The International Electrotechnical Commission (the IEC) developed the IE energy efficiency standard in order to confront the problem of nations having different standards for energy efficiency.
Metallic corrosion involves the loss of metal at a spot on an exposed surface. Intergranular corrosion occurs at grain boundaries. Intergranular corrosion is also called intercrystalline corrosion.