Not quite the cherry red zone but getting up there. I have had it up over 1300 once by accident for a very short period of time. Will try and not do that again. 1000 is about the limit I would go. I also would not attempt to maintain a 1000 temp for any serious amount of time although a properly installed chimney should have no problem handling it for a reasonable time. A good hot stack is key for good draft and control on any creosote.