Customer requested second opinion, other contractor condemned heat exchanger, upon arrival found unit off, check furnace operation combustion test ok performed smoke test did not see any change, re over evaporator coil cover and inspect exchanger did. It see any visual cracks air anything major to condemned heat exchanger, did noticed inducer making grinding noise, we will verify with manufacture if unit is under warranty, did noticed a high temp split between supply and return, both return and supply ducts are 8x10, unit could use more volume to improve efficiency and performance