Our indoor toilet had no heating when I was a child, so in frosty weather a very small parafin lamp was placed on the floor beside the waste pipe to prevent the water in the bowl and cistern from freezing.
It kept the temperature just above freezing, but did not warm the very small room, so we did our business fast!
We had stone pigs and rubber hotties to warm our beds with, and when we children were sent upstairs with the hot water bottles we placed our night clothes on top of them so our nighties weren't icy cold to get into to at bed-time.
The advantage of the stone pig was that it stayed warm all night, so you could put your underclothes round it before getting into bed, so they were not cold in the morning.
I had heard of the candle in the flower-pots - I think they were still in use amongst greenhouse owners in the 1950s.