Mike,
My hangar lags behind ambient as well. Insulated doors do not hurt.
Michelle

Mike Noel wrote:

Thought I would share this experience with the group since I have worried
about cold weather starting each winter since I bought my plane.
Living in Tucson, it doesn't get cold very often, but on those mornings when
the ambient air temperature reaches freezing or below I have wondered if I
was harming the engine starting it early in the morning. I have an unheated
and unisulated hangar and use 15-50 year round.
This morning's forecast was for 30 degrees F and the ATIS was reporting 0
degrees C. After opening the hangar door I touched the concrete floor and
could tell it was much warmer than the air temperature. I placed a digital
thermometer against the front cylinder fins and got a reading of 45 degrees
F. The thermal mass of the floor and earth beneath had kept the engine at a
safe starting temperature.