and removing the doors at the front face of the combustion chamber fasteners 35 are removed to allow platform 30 and attached burner unit 27 to be removed as a single unit a different style of burner with its own attached platform can then be inserted into place according to the homeowner 39 s desires fig4 and 5 show a second embodiment of the present invention comprising a gas fireplace assembly configured as a heating fireplace with heat exchange means mounted in combustion chamber 10 of fireplace unit 8 in this configuration the fireplace assembly is a high efficiency heating unit as best shown in fig4 the second embodiment uses the same fireplace unit 8 as the first embodiment in this second embodiment burner unit 27 is mounted in a heat exchanger insert 50 adapted to be installed within combustion chamber 10 of fireplace unit 8 shelf 32 is used to secure and support insert 50 heat exchanger insert 50 comprises an enclosure having its own combustion chamber 52 insert 50 is formed from sheet metal panels that includes side panels 54 a rear panel 55 a top panel 56 and a base panel 57 the insert has an open front face 59 mounting brackets 61 are provided to position a glass panel 60 across open front face 59 the insert is shaped to correspond to the combustion chamber 10 of fireplace unit 8 there is an aperture 62.