Very old, stone, single-glazed house. Below freezing - ice on the inside of the windows, you can see your breath in the air and at its worst the plumbing has frozen up.
We're happy if/when we can achieve 16 degrees in winter. Closing the thick curtains at dusk, wearing plenty of layers including good slipper boots, throws on seating, hot water bottles, hot meals and drinks, using the oven to cook, 13.5+ tog duvets, flannelette sheets, pyjamas, dressing gowns, door curtains, draught excluders and lighting the fires, or at least a fire, all make a difference - not forgetting snuggling up with the other humans and pets.
I'm not recommending it, but equally I really wouldn't want to live in a house with the central heating on full blast and the occupants walking around in summer clothes.