-20 C, as Canadian that's when I put a sweater on :))
I think -60 C to 70c would be a good temperature range, but gravity could be a bigger issue.
Don´t forget that those are average temperatures, presumably in the middle latitudes.
Even in pre-industrial (and thus before any "climate control" other than open fires) times, people on Earth settled in places with temperatures ranging from what... -10°C to 50°C? 0°C to 40°C? And temperature varies fairly wildly by latitude, so even with more or less complete loss of technology during the Succession Wars, temperature would not a planet completely uninhabitable as long as there are latitudes in which temperatures are within the above range - the equatorial regions of cold planets, or the arctic/sub-arctic regions of hot planets.
Air pressure would also be a limiting factor - at higher pressures, low-lying regions might be uninhabitable, while at lower pressure, high altitudes might be near vacuum. IIRC the former is the case on Hesperus II, while the latter showed up on the periphery world where the Northwind Highlanders fought that Smoke Jaguar galaxy... Wayside, I think. There´ll be some planets where air pressure is too low even at sea level, and some with high air pressure and few or no highlands far enough up to provide sufficiently low air pressure, but those probably won´t be many. Well, there will be many worlds with too low an air pressure, but few of those will have complex life because they won´t have liquid surface water.