A system includes a retention system configured to support a heat exchanger along a flow path within a duct. The retention system includes a first sleeve configured to extend between opposite first and second walls of the duct, a first cable extending through the first sleeve, and a first bumper coupled to the first sleeve. The first bumper is configured to contact the heat exchanger. The retention system includes a first tensioner coupled to the first cable, wherein the first tensioner is configured to provide a first tension in the first cable. The first tension is adjustable to detune the natural frequency of the heat exchanger away from any excitation load frequencies caused by an exhaust gas flow through the duct.