Abstract: Combustion products having water vapor mixed therewith are conducted along a helical path by a heat transfer conduit in surrounding relation to a cylindrical cooling zone. A blower at one axial end of said cooling zone induces an axial inflow of air that is radially discharged through the gaps between adjacent coil sections of the heat transfer conduit causing condensation of the water and entrainment therein of noxious components of the combustion products. Additional cooling may be provided through an evaporator coil within the cooling zone.