This is a cute idea as long as one has a very cheap source of candles or other non-obnoxious things to burn indoors.
Here's another idea for keeping comfortable if anyone is interested...
For over 7 years I lived in a tiny camper in mid-northern Vermont all year 'round.
My ancient camper was under a portable garage which did help keep things a bit better insulated - but as many will know, camper walls are only about 1" thick and this one was 50+ years old and built of all wood/metal - for summer usage only.
It had no furnace or any heat source.
The main heat for me was a 1500 watt electric heater since it really was quite tiny in there and I don't need much heat.
However that left me olde legs & feet quite chilly when I was sitting at the table (for one) in the cooler times of year.
My 'secret' was 2 things that used together fixed the problem very well.
The 1st was some black leg warmers from the $1 store - added over socks and bootie slippers.
The 2nd was just a $10 electric heater pad (the kind used for a sore back, etc...).
I would rest my feet on that.
It used very little electricity.
Even when it was below zero these things kept me comfortable inside that old camper.
Back to the idea in this thread=>
Another, perhaps safer variation of the clay pot idea might be just to put a 100 - 300 watt incandescent light under pots.
I bet that would cost less than buying candles and would have no open flames or fumes to worry about.
Edit:
I now see this page=>http://heatstick.com/_KanHeet01.htm
Has electric variations, but it is still rather spendy.
I try to make stuff like that for cheap, to avoid spending so much $$$.