I recently did some testing of gas temperature vs pipe temperature due to questions raised in this thread. Here are the results of my testing (also found in thread above). I just checked the difference between flue gas temp and pipe temp on my stove - the gas temp on the Condar probe was 900F and the IR thermometer showed ~400 on the pipe right next to the Condar. The fire has been going for several days, so the pipe has had plenty of time to “get up to temp”. It is single wall flex ss, painted flat black, so it’s not a reflectivity issue with the IR therm. Being the suspicious type, I inserted a K type thermocouple (attached to my multimeter) along side the Condar. The Condar was about 250F higher than the thermocouple. After testing the thermocouple in ice water and boiling water (within a degree F on each), I adjusted the Condar to match. On the latest check, I had 600F on both the Condar and the thermocouple and 330F on the IR thermometer. So unless the IR is way off (which it doesn’t appear to be based on some tests), there is still a significant difference between the gas and pipe temps. The temperature right next to the inside of the pipe, but away from the probe hole (to keep room air from blowing on the thermocouple) was 425F when it had been 600F in the center of the flue. It would appear that a laminar flow exists and the hotter gases are toward the center of the flue.