Abstract: A modular ignition assembly for use in a direct fired make-up heater, includes a hot surface igniter disposed adjacent the discharge ports of a pilot tube for providing a pilot flame. The hot surface igniter is surrounded by a tubular shroud for minimizing the effects of cold air and high humidity on the performance of the ignition assembly. A flame sensor is provided for detecting and a sensing the existence of pilot flame and for controlling the gas flow to the burners accordingly.

Abstract: A plurality of planar walls for a HVAC enclosure enclose an interior volume subjected to negative pressure which pressure tends to draw undesirable contaminants into the volume through fastener apertures used to attach the walls together. A corner joint construction for the enclosure includes inner and outer L-shaped members formed with tortuous engaged end extensions. The members cooperate to form an L-shaped volume for the length of each corner joint of the enclosure and an end chamber also extending for the length of the joint is formed by the extensions at each L-shaped volume leg edge. The L-shaped volume and the end chambers isolate the outermost member from interior volume. Fasteners used to fasten the walls to the corner joint are fastened in communication with the end chambers or the L-shaped volume to isolate the interior volume from the fastener apertures.