How did people stay warm?
We can say that first step was that people simply “shrunk“ their living space.
For example, if a family of people had a house with six rooms they simply stopped using four rooms, and they lived in two rooms only, because of a simple reason – it was easier to heat two rooms only.
To get wood for heating was a hard process and often dangerous, so how much fuel you spent in your home was a matter of staying alive.
Comfort was completely forgotten because of necessity.
Also people insulate their homes with what they had. A majority of windows were crushed (glass) because of detonations (shelling), so people blocked window openings with what they had.
Blanket, pillows, nylons, and tarps were used for that. Also, duct tape was a very useful item.
Homes were kinda rearranged in order to make it more energy efficient in very rudimenrtary ways. For example, if a house had smoke exhaust just in the kitchen but that kitchen was not good for having wood stove there, then simply stove was moved from that kitchen into the desired room. A hole was made in that room (for smoke exhaust) and the stove was put there.
You need to understand that homes (houses, apatments) when SHTF were very fast to deteriorate. There was no service to call, remember. Leaks from the roofs, freezing temperatures… all that makes your house quite problematic to live in. We were trying to fix what we could, but insulation was problematic very quickly. A lot of problems could have easily been solved with simple items like insulation foam (in spray containers) for example, but nobody was prepared for SHTF. (Yes, I have it now)…