I agree, no space heater. I don't have a thermometer, I just go by the water pan. A little ice on the pan is fine. If it puts a heavy layer on, then I worry about my birds combs. Since you have two hens - more birds keep themselves warm - and daylight they do quite fine in the cold as they mill about and they keep warm that way. When it does get cold enough to really freeze their water source, I tuck them into nesting boxes with a flap over them at night after they roost. I use a burlap sack - towel or rag will suffice - and hang it over the opening of the nesting box, but not completely covering it, leaving the bottom edge above the setting box lip. That way in the morning they can come out on their own. This small space conserves heat and prevents any freezing of combs, wattles, toes.
