the plate receptive center portion of the housing are defined by four angle irons q for engaging the four corner adjacent portions of each of a plurality of alternate plates a and b it should be understood that if the first plate to be inserted into the central portion of the housing is plate b followed by plate a the spacing between the forward wall 64 of plate a and rear wall 66 of plate b will define a passageway y for the passage of ambient air it should be understood that the abutment forming in turned side edges of plate a are adapted to abuttingly engage the entire height of forward surface 64 of the next adjacent plate b and it will be further noted that the abutment forming in turned upper and lower edges of plate b are adapted to engage the entire width of forward surface 64 of plate a immediately adjacent the ends of abutment members 80 it will also be noted that the length of abutment members 80 are less than the overall height dimension of plate a by a dimension which approximates the vertical spacing between the in turned portions 72 of said abutment defining means with particular reference now to fig1 and 2 it will be noted that the lint and moisture laden hot exhaust gases from conduit 18 passing upward through stack 22 will pass in an uninterrupted manner through the first set of passageways u as defined by the laterally spaced adjacent surfaces 64 and 66 of adjacent plates a and b it will likewise.