I use the smell technique when I go in the TV room and get distracted and forget to flip the damper or turn the stove down. I have a magnetic thermometer on my stove pipe adapter and the smell starts when it's above 500. Don't know what the actual flue temp is but 500 is the temperature of smell as my wife puts it.I just posted about that in another thread. If I wouldn't have had a flue temp monitor, the only way I would have known my flue was way too hot would have been from the hot metal smell.