Systems and methods include heat exchangers using Organic Rankine Cycle (ORC) fluids in power generation systems. A system for power generation using an ORC comprises: a heat exchanger configured to be mounted entirely inside a duct, the heat exchanger comprising a single inlet which traverses from an outer side of the duct to an inner side of the duct, a single outlet which traverses from the inner side of the duct to the outer side of the duct, and a conduit connecting the single inlet to the single outlet, the conduit being provided entirely inside the duct.