Abstract: A heat recovery steam generator system which includes a plurality of side waterwalls defining an enclosure and a waterwall divider extending within the enclosure to define first and second chambers within the enclosure. The first chamber has an inlet and an outlet; and the second chamber has first and second inlets and an outlet, the first inlet of the second chamber is in fluid communication with the outlet of the first chamber, and a plurality of boiler bank tubes extend through the second chamber. Some forms of the invention have ducting for connecting the exhaust of an associated gas turbine partially to the inlet of the first chamber and partially to the second inlet of the second chamber. A plurality of burners may be disposed at the inlet of the first chamber and the system may also include a forced draft blower for blowing ambient air and ducting coupling the forced draft blower to the inlet of the first chamber.