compartment 72 a power transformer 24 which receives electrical power from the primary source of electrical power 24a is mounted on the second compartment cover 38 and operatively extends into the second housing compartment 32 for connection with the electrodes 23 of the igniter 22 the construction of the furnace 10 can be best seen in fig1 3 the front wall 16 of the cabinet shell 19 is provided with the front door 11 pivotally mounted thereto for pivotal movement as shown in phantom in fig1 the heat exchanger 40 includes an upper bank 41 of conduits 42 oriented generally parallel to the longitudinal orientation of the burner chamber 15 these conduits 42 pass through the ventilation chamber 13 in a spaced apart configuration to allow ambient ventilation air to flow therebetween the heat exchanger 40 further includes a lower bank 43 of conduits 44 oriented generally parallel to the both the burner chamber 15 and the upper bank 41 these conduits 44 also pass through the ventilation chamber 13 in a spaced apart configuration to allow ambient ventilation air to flow therebetween to seal the flow path for the combustion gases from the ventilation chamber 13 the furnace 10 uses header walls 46 47 and 48 which in conjunction with the respective walls of the cabinet shell 19 define header areas 51 52 and 53 in which the combustion gases are required to make abrupt right angle turns within the flow path the first header wall 46 extends around the burner chamber 15 and around the distal ends of each of the conduits 42 in the upper bank 41 accordingly the first header 51.