hvaceric doing training on combustion analysis. We took a Heil 80 that we removed from a home. The competition said it had cracks but the HX was sound as can be. We hooked it up to our gas line and vented in 5" single wall to the 4" b-vent for our tube heater.
Picture 2 shows the 5" flue about 80% blocked. Did it bother the pressure switch?
Picture 3 says no. Pressure switch opens at .65" WC while the manometer says .81 so despite the horribly blocked flue, furnace kept purring along.
Picture 4 shows the draft gauge after the block. Very strong draft. Between the inducer and the block, the flue went positive meaning exhaust could come out any joints in the pipe. CO production went up with this blockage too.
Picture 5 shows a hole Eric drilled in the HX. It affected nothing. CA readings stayed the same as did draft. We had the burner door on top of the outlet providing some static pressure.