Abstract: The heater includes a jacket unit connectable to the cooling system of an internal combustion engine, the jacket unit forming a central cavity in which a catalytic burner unit is suspended by means of a bolt that extends upwardly through an upper opening in the jacket unit. Overlying the jacket unit is a perforated dome-shaped cap having a hole through which the bolt extends so that a nut applied to the upper end of the bolt clamps the perforated cap against the upper end of the jacket unit, at the same time suspending the burner unit within the jacket unit's cavity. Within the cavity is a fixedly positioned ring through which the bolt extends, the bolt having a collar that abutts the underside of the ring when the nut is fully tightened. The catalytic burner unit also includes a feed tube extending downwardly therefrom. A second perforated dome-shaped cap underlies the jacket unit having a hole through which the feed tube extends. A sleeve of catalytic material is included in the burner unit.