Reliable temperature range for pixhawk 1 hardware? what is the minimum safe air temperature?

winter here is cold. I understand pixhawk 2.1 added a heating element to it’s IMU to extend it’s operating temperature. What about a pixhawk 1 with no such heater - what is the lowest air temperature that it can reliably operate at? And what happens if I go below that - does it fail, or do it’s measurements just drift with temp? I mean, is it only a problem if I calibrate it when warm, then fly it until it gets cold?