Budget Shed Heater

It's getting cold. There's no getting away from the fact. The sun isn't getting as high in the day and there's more cloud to cover it.
So it's time to find an alternative to my electricity drinking heater.
I found a candle powered heater via Google on YouTube but it didn't seem to work too well. It worked ok but gave off too little heat.
Then I hit the mother load. I found a reprint of a World War 2 information leaflet which showed a similar heater using two flower pots and a candle to heat Anderson shelters.
You need two terracotta pots and a candle. Stand the larger pot on too wooden blocks. This is to keep the base hole clear. Put the candle in the lower pot and light. It's best to use a long reach lighter for this. Put the smaller pot on top upside down.
After a few minutes the pot was radiating some steady usable heat and a stream of hot air blowing out the top. The temperature of the air was reading 140°c out of the upper hole. After about half an hour I had a toasty shed and no massive electricity bill.
Now if I could just run my router from a candle........