Why Is My Candle Tunneling and Can I Fix It?

Tunneling is when a candle burns straight down the middle and leaves a ring of unmelted wax against the jar. It is caused by one of two things: the candle was blown out before the melt pool reached the edge, or the wick is too small to heat the whole surface. Which one it is decides who fixes it, the customer or the maker.

What causes tunneling?

Makesy lists these causes:

• A short first burn. Makesy says wax "solidifies in the exact pattern in which it last melted." Each burn repeats the first, so a short first burn makes a tunnel that gets deeper. They call blowing out before the pool reaches the edge the number-one cause.
• A wick that is too small. In their words, it "simply cannot generate enough heat to melt wax all the way to the edges."
• Harder wax. Some paraffin blends need more heat to melt fully.
• An off-center wick. If the wick moved while the candle set, one side heats more than the other.
• Drafts and cold rooms. Moving air tilts the flame, and a cold room makes the flame work harder.

How do I tell a first burn problem from a wick problem?

Look at the first burn. If the candle tunnels even when it burns long enough on the first light, the wick is too small for the jar, and no habit of the customer will fix it. If it burns to the edge on the first light but tunnels after, something cut the first burn short or the candle sat in a draft. A maker finds this out in testing, before selling. Our wick size guide shows the process.

How long should the first burn be?

Makesy suggests one hour per inch of jar width. A 3 inch (7.6 cm) jar gets about 3 hours, and a 4 inch (10 cm) jar about 4. CandleScience says that if the pool is not at the edge, let the candle burn 3 to 4 hours at one lighting. Put the burn time on your care card, and ask customers to burn long enough to reach the edge. Never leave a candle burning out of sight.

Worked example: how much wax is stuck?

For a straight-sided jar, the melted surface area scales with width squared. Say a 3 inch jar develops a tunnel only 2 inches wide.

• Melted share: (2 / 3)² = 4 / 9 = 44 percent of the surface
• Stuck share: 1 - 0.44 = 56 percent

If the tunnel stays that narrow all the way down, more than half the wax never burns. That is a rough picture from geometry, not a measured result, but it shows why a customer feels cheated.

Can I fix a tunneled candle?

Often, partly. These are the fixes Makesy lists:

• Foil. Make a collar of aluminum foil around the top of the jar with an open hole above the wick, so the foil is not touching the flame. The foil reflects heat onto the hard ring. Makesy says to burn for one to two hours, then remove the foil once the pool is even. The foil gets hot, so use tongs after the flame is out and the foil has cooled.
• Heat gun or hair dryer. With the candle unlit, aim a heat gun or hair dryer on a low setting across the top, keeping it moving, until the outer ring is level with the center. Then relight and burn a full session. Never hold the heat still on one spot.
• Scoop and re-pour. For a bad case, take out the hard outer wax, melt it separately, and pour it back once the surface is level.

If the cause is a small wick, these fixes only buy time. The next batch needs a bigger wick.

How do I prevent it in my own candles?

• Test at least three wick sizes in each jar, per Makesy, before a production run.
• Test with your actual wax, oil and dye, since fragrance can change melt behavior.
• Trim wicks to about 1/4 inch (6 mm) before each burn.
• Keep the wick centered while the wax sets.
• Print a first-burn instruction on the care card.
• For jars wider than 3.5 inches (9 cm), test a larger wick series or a multi-wick setup.

Common mistakes

• Blaming the customer when the wick is too small.
• Changing wax or oil load without retesting the wick.
• Using a chart size and skipping the test.
• Telling customers to burn a "few hours" with no width-based number.
• Fixing tunneling with a heat source and then leaving the room.

Questions

Does tunneling make a candle unsafe?

Tunneling by itself is a performance problem. CandleScience notes that an under-wicked candle's flame may go out before the wax is used up. Keep burning within sight and put the flame out if anything looks wrong.

Why does my candle tunnel only on the second burn?

Usually the first burn did not reach the edge, and the second burn repeated the same narrow pool. The wax remembers its last melt pattern, as Makesy puts it.

Can I just use a bigger wick to stop all tunneling?

Not blindly. A wick that is too big gives a tall flame, soot and a hot jar. Move up one size and retest, and watch the jar heat and the flame.