Why Is My Candle Flame Too Big or Flickering?

A flame that is too big or will not hold still usually comes from one of three things: a wick that is too long, a wick that is too big for the jar, or air moving across the flame. The National Candle Association (NCA) says a candle that keeps flickering or smoking is not burning properly and should be put out. Let it cool, trim the wick to 1/4 inch (6 mm), move it away from drafts, and relight. If it stays tall, the wick is too big. Test in your own jar with your own wax, and never leave a burning candle unattended.

What should I do right now?

1. Put it out. The NCA suggests a snuffer or a gentle breath, and says to wait until the wax has fully cooled before you touch the candle.
2. Look at the wick. A long, crooked or mushroomed wick can make a big flame. The NCA says long or crooked wicks and debris in the wax can make the flame flare up, and that a wick that has mushroomed from over-burning can produce a dangerously large flame.
3. Trim to 1/4 inch (6 mm) with wick scissors, and take out any debris, as the NCA says.
4. Move it away from drafts. Fans, vents, open windows and walkways disturb the flame. CandleScience says an excessively moving flame may be a draft, so retest in another spot.
5. Relight and watch. If it still flares, put it out for good and size the wick down next time.

How big should the flame be?

The numbers differ by source, so I list them.

I could not open the paid text of ASTM F2417, so I am quoting Armatage, not the standard. Armatage names the 2017 edition, ASTM's store now lists F2417-26 as active, and I could not check whether those limits changed. The CandleScience burn test page also says the flame may move a bit more near the end of a burn, because heat builds in the jar as the wax level drops.

What are the causes?

• Wick too long. Lone Star lists a tall, flickering flame as a wick that is too large or not trimmed to the proper length. The fix is to trim it, or size down one step and retest.
• Wick too big. CandleScience lists a flame that is "too tall and flickers continually," a deep melt pool, mushrooming, soot and a hot container as signs of an over-wicked candle. See our guide on wicks that are too big.
• Drafts. The NCA says moving air disturbs the flame's teardrop shape, and soot escapes as smoke.
• Burning too long. Lone Star lists a candle left to burn too long among the causes of mushrooming, and the NCA says a mushroomed wick can make a dangerously large flame.
• Two flames in one jar. In CandleScience's coconut-soy lab notes, double CD wicks in large jars gave taller flames that sometimes flickered into the glass, while double LX wicks kept flames small and tight. See our guide on two or three wicks.

Worked example: a flame log

Measure the flame at each hourly check with a ruler held at a safe distance, and write it down. All numbers are examples.

The untrimmed candle rose 2.75 - 1.50 = 1.25 inches over 3 hours, about 0.42 inch an hour. It went over CandleScience's 2 inch mark at hour 3 and ended close to the 3 inch line Armatage quotes. The trimmed one rose 1.50 - 1.00 = 0.50 inch, about 0.17 inch an hour, and ended 1.25 inches lower: 1.25 / 2.75 = 0.45, or 45 percent. Trimming fixed most of it here. If the trimmed candle had still climbed past 2 inches, the next step is one wick size down. In a real test, do not let a climbing flame run just to fill in the table. If it keeps flickering or smoking, or gets too close to the jar, put it out.

Common mistakes

• Trimming a lit wick, or trimming it too short or too long. Aim for 1/4 inch.
• Blaming the wick when a fan was running.
• Judging flame height at one check. Measure each hour, as CandleScience says.
• Changing the wick size and the fragrance load together.
• Leaving the candle burning to see what happens.
• Telling customers "trim as needed" without a number.

Questions

Is a flickering flame dangerous?

I cannot give safety advice beyond what the NCA says: a candle that keeps flickering or smoking is not burning properly and should be put out, and always put a candle out if the flame gets too close to the holder or container. Fix the cause before it burns again.

How long can a candle burn at a time?

The NCA says one hour for every inch of diameter on the first burn, and in general no more than four hours, with at least two hours to cool before relighting. CandleScience says not to burn past four hours, because it can overheat and break the container.

Does fragrance oil make the flame bigger?

It can feed the flame. Lone Star says a heavy fragrance and dye load can cause mushrooming, and CandleScience says a high load can cause excess soot. Change the load and the wick one at a time and retest.