An air removal unit for removing exhaust air from an equipment rack or enclosure, the unit comprising: a housing defining an interior chamber; the housing having a front panel, an upper back panel, a lower back panel, and two side walls (16,18); an upper exhaust module disposed within the interior chamber and comprising a fan coupled with a first internal air plenum (50A,50B) defined by an interior wall disposed within the housing that extends vertically and parallel to the front panel, the side walls (16,18) and the upper back panel; a lower exhaust module disposed within the interior chamber and comprising a fan coupled with a second internal air plenum (52A,52B) defined by the side walls (16,18) and the lower back panel; and the upper exhaust module and the lower exhaust module being further disposed in a stacked configuration along the depth of the unit, characterised in that the upper exhaust module includes: at least one upper fan module (28A, 28B) removably secured to the upper back panel, the or each upper fan module (28A, 28B) including said fan coupled with the first internal air plenum (50A,50B); and in that the lower exhaust module includes: at least one lower fan module (30A, 30B) removably secured to the lower back panel, the or each lower fan module (30A,30B) including said fan coupled with the second internal air plenum (52A,52B); the housing further comprising a lower exhaust module front panel positioned behind the front panel, and the second internal air plenum (52A,52B) being further defined by the lower exhaust module front panel, and wherein the lower back panel and the lower exhaust module front panel extend along parallel planes that are at an acute angle with respect to a generally vertical plane defined by the upper back panel to accommodate a depth of the upper fan module (28A,28B). a housing defining an interior chamber; the housing having a front panel, an upper back panel, a lower back panel, and two side walls (16,18); an upper exhaust module disposed within the interior chamber and comprising a fan coupled with a first internal air plenum (50A,50B) defined by an interior wall disposed within the housing that extends vertically and parallel to the front panel, the side walls (16,18) and the upper back panel; a lower exhaust module disposed within the interior chamber and comprising a fan coupled with a second internal air plenum (52A,52B) defined by the side walls (16,18) and the lower back panel; and the upper exhaust module and the lower exhaust module being further disposed in a stacked configuration along the depth of the unit, at least one upper fan module (28A, 28B) removably secured to the upper back panel, the or each upper fan module (28A, 28B) including said fan coupled with the first internal air plenum (50A,50B); at least one lower fan module (30A, 30B) removably secured to the lower back panel, the or each lower fan module (30A,30B) including said fan coupled with the second internal air plenum (52A,52B); the housing further comprising a lower exhaust module front panel positioned behind the front panel, and the second internal air plenum (52A,52B) being further defined by the lower exhaust module front panel, and wherein the lower back panel and the lower exhaust module front panel extend along parallel planes that are at an acute angle with respect to a generally vertical plane defined by the upper back panel to accommodate a depth of the upper fan module (28A,28B).