A heat exchange flue, comprising a top flue gas chamber, a bottom flue gas chamber and a heat exchange section located between the two chambers (1, 10), the heat exchange section comprising a heat exchange tube bank in the middle and a left side flue and a right side flue respectively on the left and right sides of the heat exchange tube bank; wherein the top flue gas chamber is defined by the surrounding flue walls, which collects upstream flue gas and allows the flue gas to flow into the left side flue and/or the right side flue, and the bottom flue gas chamber is also defined by the surrounding flue walls, which collects flue gas from the left side flue and/or the right side flue, and discharges the flue gas downstream, and the left and right side flues (5, 12) are each in a vertical box shape, defined by the surrounding flue walls and the heat exchange tube bank; the left and right side flues (5, 12) each have a plurality of flue gas dampers, and the flue gas dampers in each side flue are vertically spaced apart, and the flue gas dampers in the left side flue are horizontally aligned with the corresponding flue gas dampers in the right side flue, each flue gas damper has a flue gas damper frame defining a flue gas port and has a flue gas port opening and closing device capable of selectively opening and closing the flue gas port; wherein each flue gas damper frame is hollow out and is horizontally arranged, and has an outer contour consistent with the cross-sectional shape of the left or right side flues (5, 12), the peripheral edges of the flue gas damper frame being respectively connected to the surrounding flue gas walls in an airtight manner, the part of the flue gas damper frame corresponding to the heat exchange tube bank being connected to a substantially horizontal flue gas shield plate in an airtight manner; each flue gas shield plate has its front and rear sides air-tightly fixed to the corresponding front and rear flue walls, and has its left and right sides air-tightly connected to the corresponding left and right side flue gas damper frame respectively, so that each layer of the left and right side flue gas dampers and the corresponding flue gas shield plate, in combination with an adjacent layer of the left and right side flue gas dampers and the corresponding flue gas shield plates, define a horizontal flue section; the heat exchange tube bank is oriented to intersect with, or not intersect with any of the flue gas shield plates plote; in case that the heat exchange tube bank is oriented to intersect with a flue gas shield plate, this the- flue gas shield plate is formed with holes to receive the heat exchange tubes in an airtight manner. wherein the top flue gas chamber is defined by the surrounding flue walls, which collects upstream flue gas and allows the flue gas to flow into the left side flue and/or the right side flue, and the bottom flue gas chamber is also defined by the surrounding flue walls, which collects flue gas from the left side flue and/or the right side flue, and discharges the flue gas downstream, and the left and right side flues (5, 12) are each in a vertical box shape, defined by the surrounding flue walls and the heat exchange tube bank; the left and right side flues (5, 12) each have a plurality of flue gas dampers, and the flue gas dampers in each side flue are vertically spaced apart, and the flue gas dampers in the left side flue are horizontally aligned with the corresponding flue gas dampers in the right side flue, each flue gas damper has a flue gas damper frame defining a flue gas port and has a flue gas port opening and closing device capable of selectively opening and closing the flue gas port; wherein each flue gas damper frame is hollow out and is horizontally arranged, and has an outer contour consistent with the cross-sectional shape of the left or right side flues (5, 12), the peripheral edges of the flue gas damper frame being respectively connected to the surrounding flue gas walls in an airtight manner, the part of the flue gas damper frame corresponding to the heat exchange tube bank being connected to a substantially horizontal flue gas shield plate in an airtight manner; each flue gas shield plate has its front and rear sides air-tightly fixed to the corresponding front and rear flue walls, and has its left and right sides air-tightly connected to the corresponding left and right side flue gas damper frame respectively, so that each layer of the left and right side flue gas dampers and the corresponding flue gas shield plate, in combination with an adjacent layer of the left and right side flue gas dampers and the corresponding flue gas shield plates, define a horizontal flue section; the heat exchange tube bank is oriented to intersect with, or not intersect with any of the flue gas shield plates plote; in case that the heat exchange tube bank is oriented to intersect with a flue gas shield plate, this the- flue gas shield plate is formed with holes to receive the heat exchange tubes in an airtight manner.