We just purchased a used log burner. It has a six inch outlet and the space we are hoping to put it is in place of the old boiler that used to be in this property. The old pipe for the boiler flue is still in situ but is only a five inch diameter...is there anything we can do to safely fit this burner. I've hopefully attached a photo to show the pipe that's in situ. Any advice would be so welcome. Thanks