I was out today installing a secondary h/x in a 8 year old bryant 90 furnace. 2 stage, variable inducer and blower. I guess there has been some problems with these h/x. Well any way my problem is the burners. when the burners come on(low fire) sometimes one or two of the burners will have flame all the way back to the orfice causing the burner to get red hot and orange flame. if i blow on it, it will go back to normal, in front of burner cone. this fluctuates between all the burners. sometime it may not do it at all. at high fire, its fine. dont get it inlet pressure 12.5" outlet 4.9", intake air ok. its gonna soot it up if it stays this way. Any tips? I installed primary and secondary h/x. Are these junk or what?