How do we know that they aren't talking about surface temps of the stove? Or worse yet, that they just aren't very good at math and got caught in the somewhat easy to fall into trap of assuming since the outside of the pipe is 50% of the inside that the inside should be 50% of the outside. Who even knows anymore since condar makes pretty much all of the probe meters and their accuracy is now suspect? I would no sooner believe their instructions than would I believe their meters reading. I still expect the outside of the single wall to be half of the internal temp. This would be verified by noting that the overfire temp on the rutland is 550 which should correspond with 1000 internal temps which is the overfire temp for metal pipe.