Abstract: Apparatus for measuring the particulate content of a gaseous medium includes temperature control devices for permitting application to both hot gases and cold, wet gases. Specifically, the apparatus comprises an exhaust nozzle for coupling with a duct through which gas passes; a filter housing including a filter; an exhaust tube, having a heat exchange passage therein, connected between the nozzle and the filter housing; an exhaust device; a conduit for coupling a heat exchange medium to the exhaust tube passage; and a controllable heating element for heating the heat exchange medium in the conduit between a source and the exhaust tube. In preferred embodiments, the heating element is arranged around the filter housing in heat exchange relationship with the conduit, providing temperature conditioning of both the medium and the filter housing in a very compact apparatus. In a specific example of this embodiment, the heating means and the conduit are arranged in interlaced helices about the filter housing.