The wick drinks its own fuel
Why Does a Candle Burn for Hours?
A candle makes its own fuel supply: the flame melts the wax, the wick draws it up, and the heat turns it to gas.
-
Step 1 of 5
Wax molecules are middle-sized chains.
Short carbon chains are gases, long ones are hard plastics. Wax sits in between — solid when cool, but melting at a temperature a small flame can reach.
-
Step 2 of 5
The wick is not the fuel.
The wick is a bundle of twisted cotton fibres. Its job is to carry liquid wax upward into the flame, which it does through the gaps between its fibres.
-
Step 3 of 5
It is the wax gas that burns.
Liquid wax reaching the top gets hot enough to become a gas, and it is that gas which meets the air and lights. Solid wax will not catch at all.
-
Step 4 of 5
The loop keeps itself in balance.
A bigger flame melts more wax, and the wick can only draw so much. That limit is what keeps a candle burning at a steady size for hours.
-
Step 5 of 5
The wick curls into the flame and burns away.
A well-made wick bends outward as it burns, into the hottest, most oxygen-rich edge, where its tip is burnt off. That is why it never needs trimming.
A household candle gives off roughly 80 watts of heat — about the same as a person sitting still, and about a tenth of it as light.
The short version
The wick is not the fuel, and solid wax will not catch — what burns is vapour. The wick can only draw so much, which holds the flame steady, and it curls into the hottest edge and burns its own tip away.
Try it yourself
Blow a candle out and watch the wick smoke. That white trail is wax gas the wick is still making, with nothing left to light it.