Abstract: A spacer (7) for an air heater comprises a predefined number of planar walls (13; 113) that are substantially parallel and are connected two-by-two by folds (15). The planar walls (13; 113) include a plurality of louvers (171, 172) that are substantially inclined relative to the general plane (P) defined by the planar wall (13; 113). The planar wall (13; 113) further includes at least one strap (19; 1191, 1192, 1193, 1194) having longitudinal sides (21) that extend parallel to the planar wall (13; 113) and lateral sides (23) that are linked to the planar wall (13; 113) by means of at least one connecting rail (24). An air heater comprises a heat exchange bundle comprising a stack of parallel tubes (5) for the circulation of the fluid, the tubes having the width (l1) of a tube, and a plurality of such spacers (7) disposed respectively between two tubes (5).