A bottom assembly unit for a vaporizing burner combustion chamber assembly unit, especially for a vehicle heater, includes a bottom part (24) with a bottom wall. A porous evaporator medium (44) at least partially covers the bottom wall on a front side (42) positioned such that it faces a combustion chamber (20). A ring-shaped holding part (34) has a contact area (40) touching the porous evaporator medium (44). The contact area has a holding section (62) extending radially inwardly from a holding part circumferential wall (36) and extends over the porous evaporator medium (44) in a radially outer area (66). A plurality of contact projections (68) are arranged at spaced locations from one another about the longitudinal axis and extend in the direction of the porous evaporator medium. The porous evaporator medium (44) is pressed by the contact projections (68) in a radially outer area (66) against the bottom wall.