A paraffin heater.
We had no central heating in our house and no heating upstairs of any kind, bar the paraffin heater in the bathroom that only went on a bath night in Winter. It was freezing upstairs in the Winter, ice on the inside of the windows was common and I used to get dressed under the covers as it was too cold to get out of bed, but the bathroom was lovely and cosy when that heater was on. I was always a bit scared of it though!