Heat exchanger

A heat exchange unit arranged to recover heat from hot gas, the unit comprising a heat exchange duct and a bypass duct which are selectively closable, and the heat exchange duct has a number of fluid intakes thereinto wherein each intake is arranged such that when the heat exchange duct is substantially closed and fluid flows through the bypass duct fluid is drawn through the intake and into the heat exchange duct by a negative pressure created within the heat exchange duct into which each intake is connected and wherein the fluid passing through the bypass duct creates a negative pressure in the heat exchange duct.