Why a candle flame moves
A candle flame moves because of thermal convection: hot air rises, creates a current, and the flame follows that current. It's the same principle that makes smoke rise — the temperature difference generates air movement, and the flame responds to that movement.
When the flame moves erratically or excessively, the problem can be in the environment (draughts) or in the candle itself (the wrong wick). Identifying the cause determines whether you need to change where you keep the candle or whether the problem lies in how it's made.
How Convection Works in a Candle
Once you light a candle, you'll see the flame never stays completely still. The flame heats the air around it. Hot air weighs less than cold air, so it rises. That rise creates a convection current: cold air enters at the base to replace the hot air leaving above.
This current is constant while the candle is lit. A completely motionless flame doesn't exist — it always has a minimal movement because there's always convection. Hot air can't stay still.
The difference is in the magnitude of the movement. A candle in an environment without external draughts has a flame that sways gently. A candle exposed to draughts has a flame that tilts, trembles or flickers visibly. What most makers discover is that controlling the environment is as important as choosing the right wick.
External Draughts
Changing a candle's location can turn an erratic flame into a stable one. The most common cause of a flame that moves a lot is draughts in the environment. You don't need to feel the draught — a temperature difference of two degrees between two areas of the room already generates enough air movement to affect the flame.
Common sources of draughts:
- Windows with poor insulation
- Doors that open and close in another room
- Air conditioning or heating systems
- Temperature differences between rooms
- People moving near the candle
A candle near a window will have its flame moving towards the interior of the room if it's cold outside, and towards the window if it's warm. Cold glass creates a downward current; warm glass creates an upward one.
To confirm it's an external draught, move the candle to another location. If the flame stabilises, the problem was the location. If it keeps moving the same way, the problem is in the candle.
Wick Problems
The most common mistake here is assuming the problem is always the environment, when it may be the wick that causes the irregular movement. A wick that's too large creates a tall flame that consumes wax faster than the wax can melt evenly. This flame doesn't just move — it also produces black smoke and burns the candle irregularly.
A wick that's too small creates a low flame that doesn't have enough heat to form an adequate pool of liquid wax. The flame seems to "struggle" to keep going, and it moves irregularly because it doesn't have consistent fuel.
Debris on the wick also causes erratic movement. A wick with carbon residue or a deformed tip doesn't burn evenly. The flame moves towards wherever it finds fuel more easily.
Trimming the wick solves most of these problems. Put the candle out, let it cool, and cut the wick to 5-6 mm in height. A well-trimmed wick produces a more stable flame.
The question isn't whether the wick is right — it's whether it's right for that specific wax. Not all wicks work the same with all types of wax. A wick that works perfectly with paraffin can be too small for soy wax, which melts at a lower temperature.
What the Flame Height Means
The height of the flame tells you more about the state of the candle than the colour or the shape. A very tall flame (more than 2 cm) indicates the wick is consuming more fuel than it should. This can be down to a wick that's too large or to a build-up of debris. A tall flame moves more because it has more surface exposed to the air.
A very low flame (less than 1 cm) indicates the wick isn't getting enough fuel. It can be because the wick is too small or because the pool of liquid wax isn't forming correctly. A low flame moves irregularly because it "searches" for fuel.
A flame of normal height (between 1-2 cm) has a smooth, predictable movement. It moves with the natural convection currents, but it doesn't tremble or flicker erratically.
The correct height depends on the diameter of the candle. A candle 5 cm in diameter needs a larger flame than a 3 cm candle to heat the wax evenly.
When the Movement Is Normal vs Problematic
What many people don't know is that a perfectly still flame would be a sign of a malfunction, not of superior quality. Smooth, constant movement is normal. The flame sways slightly, follows the convection currents, and keeps a stable shape. This indicates the candle is working correctly.
Problematic movement includes: a flame that flickers rapidly, a flame that tilts more than 45 degrees, a flame that constantly changes height, or a flame that produces visible smoke.
A flame that moves a lot in an environment without visible draughts can indicate the wax has impurities or that the fragrance is interfering with the combustion. Very concentrated fragrances can make the flame less stable.
If the movement is problematic and isn't solved by changing the location or trimming the wick, the problem may lie in the quality of the wax or in the compatibility between wick and wax. Not all wicks work the same with all types of wax.
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FAQ
Why does my candle's flame move so much? The most common cause is draughts in the environment. Try moving the candle to another location, away from windows, doors or air conditioning systems. If it keeps moving a lot, check whether the wick needs trimming or whether it's the right size for that candle.
Is it normal for a candle flame to move a little? Yes, it's completely normal. The flame always moves because of the convection currents created by its own heat. Smooth, constant movement indicates the candle is working correctly. It's only a problem if it flickers rapidly or tilts a lot.
How do I know if my wick is too large? A wick that's too large produces a tall flame (more than 2 cm), generates black smoke, and consumes the wax very fast, creating a tunnel in the centre. The flame also moves more than normal because it has more surface exposed to the air.
What should I do if the flame moves a lot after trimming the wick? If the problem persists after trimming the wick and changing the location, it can be a compatibility problem between the wick and the type of wax, or the wax may have impurities. In handmade candles, it can also indicate the fragrance is too concentrated.