Fibrous mat type burners with elongated mats can be packaged strapped together in pairs face-to-face and enclosed in telescoping carton halves that allow for packaging burners of different lengths. Mat edges can be impregnated to block escape of combustion mixture. Burners with hat-shaped mats for enveloping and brazing heat-exchange tubes to tube sheet can be used individually or in pairs to effect such brazing on tube-and-sheet assemblies secured on rotating table and indexed into position under burners. Substrates can be heated by gas-fired burners with or without the added heating effects of the hot combusted gases generated by the burners, and with or without the flushing effects of separate gas streams. Burners can have ceramic fiber mat held over shallow combustion mixture plenum essentially completely spanned by baffle. Mats can have folded-in edges to permit close packing. Plenum can have partition forming small ignition compartment with igniter against covering portion of mat.