My grandparents' old house (~100 years old) has two rooms - an entrance/storage with a stove for cooking and a living room. The living room has the heater - a

My grandparents' old house (~100 years old) has two rooms - an entrance/storage with a stove for cooking and a living room. The living room has the heater - a very interesting contraption, it's basically a stove that heats up the whole wall and a small bed, no smoke/heat is wasted. Well in -20 degrees winters, water freezes near the windows (single glass) and entrance door. Inside it's about 15 degrees tops, but since you can sit on the heated bed, it's pretty livable (tho not by modern standards I guess). My grandmother still prefers it over the bigger new house. My main point is that in a catastrophic scenario, you can definitely do with a lower interior temp, even 10 degrees...