An analysis of the thermal response of a finned-tube, liquid-to-gas cross-flow heat exchanger due to a step change in the liquid inlet temperature is performed. Closed-form solutions for the liquid and gas temperatures as functions of space and time are obtained via the Laplace transform technique for both small and large arguments of the modified Bessel function of the first kind. Using four physically important dimensionless parameters, the response of the liquid and average gas outlet temperatures are studied and presented in the time domain. The analysts is extended to a single-row serpentine coil geometry by accounting for U-tube bends. Using a typical heat exchanger geometry, the effects of the tube bends are shown to be significant. Relevant applications include automotive and HVAC heat exchangers and systems.