Support assemblies are described herein for use with heat exchanges, wherein the assemblies are deflector and grid support assemblies having a grid support structure formed of a series of interconnected strips and having a peripheral exterior configured to be positioned within an interior surface of a heat exchanger such that the grid support structure substantially extends across a transverse cross-section of the interior of a the tube heat exchanger, wherein the grid support has a first grid support surface and an opposite second grid support surface longitudinally spaced from the first grid surface, the grid support structure defines a plurality of passageways extending therethrough from the first to the second grid support surface, the passageways being configured to support longitudinally extending tubes of a heat exchanger passing substantially perpendicularly to the first grid support surface through the passageways from the first grid surface to the second grid surface without substantially obstructing interior flow the heat exchanger; and at least one deflector plate, each having a first deflector plate surface and an opposite second deflector plate surface, wherein the at least one deflector plate defines a plurality of tube receiving openings therethrough for supporting longitudinally extending tubes in a heat exchanger, the deflector plate configured to cover at least one or more surface areas of the first grid surface to substantially obstruct flow through the deflector plate; wherein the first grid surface is configured to receive the at least one deflector plate to form a deflector and grid support assembly.