Secondaries looked like two rows of blow torches and flames being blown down across the front glass. Temperature is a thermocouple just above the clue outlet of the Jotul 350 insert. Normally runs 600 to 800 degrees F. Secondaries start around 600 or so. Temp at the bottom of the keystone looking casting on the surround just above the air outlet was over 600, as high as my IR gun will read. Impressive but kind of scary.