and enabling the heat exchanger inlet and burner outlet to be integrated and sealed against the introduction of any secondary air in addition the inlets 26 of the heat exchanger coils 24 may be fabricated as by stamping so as to have reception surfaces 70 which form a frusto conically shaped flame expansion zone 72 provision of the frusto conically shaped flame expansion zone 72 encourages creation and maintenance of the flame 34 while at the same time facilitating manufacturability moreover as will be noted from fig5 the diameter of the heat exchanger coil 24 is significantly greater than the diameter of the burner tube 30 roughly double in one embodiment to confine and yet maintain the proper flowfield for flame 34 stabilization in operation it can therefore be seen that the present invention provides a furnace 20 a burner and heat exchanger assembly 74 and a method of operation same that works with an induced draft air flow and provides reduced no x emissions the method of operation may include the steps of providing a furnace 20 or burner and heat exchanger assembly 74 as indicated above inducing air flow through the burner 30 and heat exchanger 22 using a downstream motor 50 introducing fuel flow through the fuel nozzle 42 and energizing the igniter 69 in so doing a swirling and conically expanding flame 34 is created using a single air source and thus with reduced no x emissions in addition by providing the burner 30 directly within the heat exchanger inlet 26 and providing the inlet 26 in the form of a frusto conically shaped expansion zone 72 the resulting flame 34 is both reduced in terms of no x and stable from.