Abstract: An all weather inlet/exhaust structure (32) for an outdoor furnace (10,12,14) includes a generally rectangular upper compartment (40) having an imperforate upper wall (42) and horizontally louvered, vertical side walls (44) along with an imperforate bottom wall (46) with a generally central opening (48) therein. A lower compartment (56) in the form of an inverted truncated pyramid with its upper wall being defined by the lower wall (46) of the upper compartment is provided. The lower compartment has horizontally louvered, sloped, inwardly directed side walls (58) terminating in an open bottom (60) of smaller size than the first compartment lower wall (46). A generally rectangular inlet air duct (66) depends from the lower edges of the lower compartment side walls (58) and an exhaust duct (26) is disposed within the inlet air duct (66) and extends upwardly through the lower compartment (56) to the generally central opening (48) and the bottom wall (46) of the upper compartment (40).

Abstract: Poor heat exchange in a heat exchanger between a flue gas passing through the heat exchanger and air being forced through the heat exchanger can be improved in a heat exchanger and combustor (30) for exchanging heat between a forced air stream and a flue gas generated by a plurality of spaced, parallel burners (44) with a construction including spaced, upper and lower headers (32, 34), a plurality of tubes (50), one for each burner (44) extending in parallel between and mounted to the headers (32, 34). Each tube 50 has a first section (56) of enlarged cross section adapted to serve as a combustor for fuel to generate the flue gas and a narrowed, second section (70) for exchanging heat between the flue gas and the forced air stream. Each second section includes generally flat, parallel spaced walls (58, 60) with each of the walls (58, 60) having dimples (74) therein which are directed toward the other of the walls (58, 60) into substantially contacting or almost contacting relationship therewith.