Fin conduction not only enhances heat transfer to the ambient air but also increases tube-to-tube conduction. For accurate performance analysis of plate finned-tube heat exchangers, the influence of heat conduction between neighbering tubes through the fin is numerically investigated. Governing equations for arbitrary plate fin are solved and the temperature distribution is obtained using the principle of superposition. Heat conduction between neighbering tubes and fin efficiencies are calculated by finite element method by changing the shapes of fin, the arrangements of tubes and the thermal properties of fin. Tube-to-tube conducion is known to degrade the performance of a heat exchanger. Perforated fin to reduce the tube-to-tube conduction is also tested. Perforation is found to reduce the tube-to-tube conduction significantly and thus improves the performance of a heat exchanger.