NOVELTY - The exchanger (2) has a manifold provided at an end of a cylindrical flue collector. Sets of heat exchanging tubes comprise alternating fluid flow direction and configured within an inner ring and an outer ring of heat exchanging tubes such that fluid flows through the sets of tubes and flows around entire circumference of each set of tubes before outletting from the rings of tubes. The outer ring of each tube is formed as an upstream ring of tubes configured to preheat flowing water. The inner ring is arranged downstream of the outer ring and configured to transfer additional heat to water.    USE - Tubular-type heat exchanger such as automobile radiator, air-conditioner, and steam and hot water radiators, for use in economizers and ultra-heaters in heat recovery steam generators for transferring heat from a first medium to a second medium, from first fluid to second medium and to surrounding environment.    ADVANTAGE - The economizer preheats fluid that is intended to be heated, and lowers difference between temperature of flue gases and temperature of fluid exiting the economizer so as to reduce work necessary to heat water to target temperature. The tubes of the heat exchanger are supplied with fins to increase heat transfer between flue gas and water contained within each tube. The exchanger provides a microfin to allow the tubes to be placed closer together, thus increasing velocity of gas flowing around the tubes, reducing overall size of the heat exchanger, and saving material cost since the microfin is in smaller size. The exchanger has compact economizer design or compact heat exchanger tube arrangement, thus limiting amount of space and material consumed by the entire heat exchanger. The economizer is configured as the inner ring of tubes if flue exhaust is configured to travel along the interior of the shell so as to improve heat exchanger efficiency. The tubes are made of stainless steel and hybrid of stainless steel and titanium, thus avoiding fouling.    DETAILED DESCRIPTION - The outer ring of tubes is an economizer. The manifold is an upper header (10a).    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of a tubular-type heat exchanger.    Tubular-type heat exchanger (2)    Shell (4)    Water inlet (6)    Upper header (10a)    Lower header (10b)