An afterburner for a wood stove for use as a retrofit assembly comprises a rectangular housing having openings in the upper and lower surfaces provided with cylindrical collars for cooperation with the flue duct and with the opening in the top of the wood stove respectively. The openings are positioned at the rear of the housing so as to provide a forward section spaced from the openings. A catalytic combuster mounted in a cylindrical support is movable from a position directly above the opening in the bottom surface into the front section by a manually operable handle extending through the front face of the housing. A baffle mounted on the support and arranged at a shallow angle to the horizontal overlies the major part of the combuster so as to direct gases into the front section of the housing for heat exchange contact with the walls thereof.