It's people from surrounding areas who are experiencing energy poverty. City buildings typically have either central heating or gas furnaces.

A common sight in my area at this time of the year is a senior person driving up to a community dumpster in an equally old car with plates indicating not being from around here and looking for loose pieces of wood - typically furniture.

The sale of furnaces that would even fit something like this for burning was banned in IIRC 2018, but there's a backlog of still functioning ones that are used.

Anyone trying this in a city would have the authorities called on them, but deep in rural areas few care.