My Double-Wick Candle Burns Too Hot Near the End of the Jar — Could the Container Shape Be Contributing to the Problem?

Why the end of the jar is where a double wick overheats

Jar candles tend to run warmer as they burn down. The flame sits deeper inside the glass, the walls above the pool hold warm air around it, and the pool is closer to the base. With one wick that shows up as a slightly deeper pool in the last third. With two wicks it can show up as a candle that behaved perfectly for four burns and then turns into a deep, fast pool, tall flames leaning towards the glass, and a jar too hot to pick up.

Three things make a double wick more sensitive to the end than a single wick. There are two flames' worth of heat in the same jar. Each flame sits off centre, closer to one wall than a single centred flame ever is. And the pair was chosen to reach the side walls of the widest part of the jar, so at any narrower part it is, by design, more wick than that part needs. If the jar keeps the same inside diameter all the way down, the last of those does not change. If the jar narrows, it gets worse with every centimetre.

Three container shapes that add heat near the end

1. The jar that narrows towards the bottom

This is the one the diagram draws. The table puts numbers on it: a worked-example jar, 9.3 cm inside at the fill line, tapering evenly to 7.5 cm at the inside floor, with a pair of wicks each 2.33 cm from the centre (a quarter of the top diameter, a common starting placement).

The two flames do not shrink as the pool does. By the stop line each is 1.54 cm from the glass instead of 2.33 cm, and has 23.4 cm² of pool to melt instead of 34.0 cm². For comparison, a straight-sided jar of 9.3 cm keeps 2.33 cm of clearance and 34.0 cm² per wick all the way down. That is why the same wick pair can pass in one jar and overheat in another with an identical top diameter. How to choose the diameter to wick for in a jar like this is the subject of My Jar Narrows Toward the Bottom — Should I Select the Wick Based on the Top, Middle or Bottom Internal Diameter?; how to schedule burn tests down a taper is in My Candle Jar Is Wider at the Top Than the Bottom — How Does That Affect Burn Testing as the Candle Burns Down?.

2. The jar with a thick base

A thick glass base does not change the top of the burn, but in the last third it puts both flames over a large mass of glass that heats from above, and it lifts the inside floor so the stop line sits higher on the outside than you would guess. With two flames over it, measure the base with a skewer and mark the stop line from the inside floor. The full base question is in My Jar Has a Thick Glass Base — Does That Affect How the Candle Burns Near the Bottom and Therefore My Wick Selection?.

3. The tall jar and the curved inside floor

In a tall jar the flames spend their last burns deep inside the glass, with warm air held around them. A curved inside floor, common on jars with a "curved silhouette", narrows the pool in the last centimetres the same way a taper does, only faster. Both are reasons to watch the final third closely and to stop at the line.

Measuring the shape of your jar

Listings, ours included, give an outer rim, a base figure, a "diameter" or a "width". The Clear Glass Jar with Golden Lid (150 gram) is a small example of why that matters: it lists an outer rim of 7 cm and a base of 6.5 cm, a single-wick jar whose outside is narrower at the bottom. The Apothecary Dome jar lists rim and base both at about 10 cm yet describes a "curved silhouette". Neither page tells you the inside at the bottom of the burn.

Measure the inside diameter three times: just below the fill line, half-way down, and about 1 cm above the inside floor (the stop line). Callipers with inside jaws are easiest; a strip of card cut to fit snugly across the inside works in any jar. Push a skewer to the inside floor to get the inside depth and base thickness. Then work out the wick-to-wall gap at each height: half the inside diameter minus the wick's distance from the centre. If the gap at the stop line is much smaller than at the fill line, you have found the shape contribution. If it is the same, look at wick size, trimming and session length.

What to change, in order

Steps 1 to 3 belong on your care label as well as in your tests. Steps 4 and 5 are a spacing and size trade: whatever helps the bottom can hurt the top, which is why they are tested together. If the glass runs hotter with two wicks than with one from the very first burns, not just near the end, that is a configuration question covered in My Candle Uses Two Wicks and the Glass Gets Much Hotter Than My Single-Wick Candle — Should I Change the Jar or Wick Configuration?; for a jar that is simply very hot on its final burn, with one wick or two, the jar-or-wick diagnosis is in My Candle Jar Becomes Very Hot During the Final Burn — Is the Jar Unsafe or Is My Wick Too Large?.

Spacing for a jar that narrows

A common starting placement puts each wick a quarter of the top diameter from the centre. In a straight-sided jar that holds all the way down. In a jar that narrows, it is the placement with the least clearance at the bottom. Moving the pair inwards buys clearance at the stop line and, in geometry, even brings the top's side walls slightly closer; what it costs is a longer reach to the end walls at the top.

Moving each wick from 2.33 to 1.90 cm off centre adds about 0.4 cm of clearance at the stop line (1.54 to 1.96 cm) and shortens the side-wall distance at the top slightly, but pushes the top's end walls from 2.33 to 2.75 cm away. Whether the ends still pool in 3 to 4 hours at the top is the question the test answers. The geometry of where a double-wick pool finishes last, and when a third wick makes sense, is in I'm Designing a Three-Wick Candle — How Wide Should the Jar Be Before Three Wicks Make More Sense Than Two?.

A burn-down test, costed

Worked example in the Apothecary Dome jar, 700 gm size, filled to its listed "~700 g" (weigh your own; the listing's one set of figures for two sizes means the 700 g needs checking). At 8%, each candle is 56 g of oil and 644 g of wax. A: your current pair, for example two C2 at a quarter of the top diameter from the centre. B: the same pair moved inwards. C: two C1 at the original spacing. A fourth candle duplicates the leader, costed as C2. Burn within sight, on a heat-proof surface, never unattended.

Basket notes. Apple Cinnamon is flat at ₹4.74 per gram from 50 g upwards, so three 100 g bottles cost the same per gram as a 500 g and leave less unused; its page states "6-10% for soy wax candles", so 8% in CSI 464 (up to 10% on its page) sits inside both ceilings. CSI 464 is ₹0.51 per gram at 1 kg, 5 kg and 10 kg alike, so three 1 kg bags cost ₹1,014.80 less up front than a 5 kg bag for the same per-gram price. The wicks left over (8 C1, 4 C2) cover a retest; the 76 g of oil left covers one more 700 g candle, but the 424 g of wax left does not, so a retest needs another 1 kg bag. If you own the jars, the kit is ₹3,316.68. Costs exclude labour, freight, packaging and GST.

Wicks, tools and a curved jar for the burn-down test

The step-down rung, a trimmer that reaches, bars to hold a new spacing, a stop-line reminder for customers and a curved jar to run the test in. Chosen on what the pages state, price and stock on 26 September 2026; CSI publishes no burn-down or glass-heat data for any jar and wick pairing.

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