Flue gas temperature should be measured between the barometric draft regulator or draft diverter and the flue outlet of the heating equipment. A ¼” diameter HOLE in the flue pipe (at least 6” from the draft regulator or diverter) is required. Insert the STEM through the HOLE so that the end of the STEM is not less than 2” from the wall of the flue pipe. Operate the combustion unit until the TEMPOINT reading is constant.