Well...we have lights go on in the layer coop early in the morning to stimulate laying. Last night, with single digit temps expected, we plugged in a tank heater and a heat lamp so that any gals who got really cold could take a few minutes to warm up. And of course the babies, four week old Ayam Cemanis and BCMs, have a heat lamp and my hover brooder.
Both coops are powered by a GFCI protected circuit, and apparently the tank heater shorted as it tripped the GFCI. So my babies were in an open, unheated, uninsulated coop, with no heat lamp, in single degree temps, for six hours.
Amazingly, they look fine.