My grandparents&#x27; old house (~100 years old) has two rooms - an entrance&#x2F;storage with a stove for cooking and a living room.<p>The living room has the heater - a very interesting contraption, it&#x27;s basically a stove that heats up the whole wall and a small bed, no smoke&#x2F;heat is wasted.<p>Well in -20 degrees winters, water freezes near the windows (single glass) and entrance door. Inside it&#x27;s about 15 degrees tops, but since you can sit on the heated bed, it&#x27;s pretty livable (tho not by modern standards I guess).<p>My grandmother still prefers it over the bigger new house.<p>My main point is that in a catastrophic scenario, you can definitely do with a lower interior temp, even 10 degrees...