The tealights are put inside a bread loaf tin and covered with a small upside-down flowerpot.
The hole in the top of the upside-down pot is covered with the metal casing from tealight or a small coin.
This pot is covered by a second, larger pot and the hole in the bigger flowerpot is left uncovered.
The system works because the candles produce gases full of heated particles that are captured and channelled through the pots.
These hot gas particles are lighter than the gases in the air, meaning they rise up into the colder area.
This causes the cold air to fall into the warm areas and creates a convection current which transfers heat from one pot to another, and out of the hole on top.
Do not leave the plant pot heater unattended. The plant pot will eventually get very hot so be careful not to burn yourself when you need to touch it.