We study the effect of heat transfer between the tubes of a plate-fin and tube heat exchanger by conduction through the fins. Fin conduction not only enhances heat transfer to the over-tube fluid, but also increases tube-to-tube conduction. A continuum model to evaluate this conduction is developed and conditions under which it may or may not be neglected are determined. The effect of parametric variation on the performance of a single-row prate-fin and tube heat exchanger is considered in some detail. Tube-to-tube conduction is found to degrade the performance of the heat exchanger. It is found that the same heat transfer area distributed in a different number of tubes affects its performance.