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This guide has gone through several revisions. And as much as I would enjoy writing an Alton Brown-style scientific breakdown of the entire candlemaking process, that’s not really what most people are looking for. Most people just want answers. So we’ll just get straight down to the good stuff: How do you improve the hot throw of your candle?

First, let’s start with the four factors that are most important:

1. Are you using enough fragrance oil?
2. Is your candle large enough?
3. Is your melt pool hot enough?
4. Is your fragrance oil simply not strong?

Everything else? Don’t worry about it until you get these three things dialed in. Switching wax types? The temperature that you pour the wax? The temperature that you mix in your fragrance? The amount of time you spend mixing? How long you cure from? Tweaking these prematurely is like tweaking the aerodynamics of your race car: sure, they might improve performance a bit, but if your engine is faulty, that should be your first priority.

TL;DR:

1. Are you using enough fragrance oil? If you're not using 10%, use 10%.
2. Is your candle large enough? A 2" candle will fill a bathroom. A 3" candle will fill a bedroom. A 4" candle will fill a living room. If your container is too small, either go bigger or light multiple candles.
3. Is your melt pool hot enough? If your melt pool doesn't reach the edge of your container or if your melt pool isn't ~145F+ at the edges of your container, you need a larger wick.
4. Is your fragrance oil simply not strong? Heat up pure FO to 150F and let it stay there for an hour. If it's still not strong enough, then you need a new FO. If you really love the scent, you can juice it up with essential oils and aromachemcials, see below.

Are you using enough fragrance oil?

How to test for it:

Easy. Are you using 10% fragrance load? And are you happy with your hot throw? If the answer to both these questions is “No”, then that means you’re not using enough fragrance oil.

How to fix it:

Also easy. Use 10% fragrance load. If you’re still unhappy, take a look at the candle size (see below).

What's the science behind it?:

Most wax manufacturers recommend a maximum fragrance load of 10%. But this isn’t a hard-and-fast rule. These instructions are sort of like the instructions on the back of a box of cake mix. Both the instructions and the cake mix itself are designed to work for all fragrance oils, all wick sizes, for all people, in all places, of all levels of intelligence and ability, and are meant to have very large margins of error. In other words, the manufacturer’s guidelines are not optimized for maximum performance, they’re optimized for maximum flexibility.

What this means is two things: first of all, if you know what you’re doing, you can exceed 10% fragrance load. But don’t. If you need this guide, that means you’re not there yet. But what it also means is that there is very little good reason NOT to use 10%, especially if you’re unhappy with the hot throw of your candle. It’s important to note here that changing the proportion of fragrance oil in your mixture will affect the behavior of the final factor in determining your hot throw: the size and temperature of your melt pool.

Is your candle large enough?

How to test for it:

Measure the diameter of your candle at the top (either in millimeters or inches). Then calculate the following

• (Metric): Fragrance Load % * ( 8 * Candle Diameter in mm - 300 ) = Coverage in Square Meters
• (Yankee): Fragrance Load % * ( 2150 * Candle Diameter in inches - 3250) = Coverage in Square Feet

So for example, a 65mm / 2.5in candle at 6% fragrance load:

• (Metric): 6% * ( 8 * 65mm - 300) = 6% * 220 = 13.2 Square Meters
• (Yankee): 6% * (2150 * 2.5in - 3250) = 6% * 2125 = 127.5 square feet

Estimate the size of the room you’re trying to fill. Is your room significantly larger than the coverage of your candle? If yes, then your candle is too small.

How to fix it:

If you’re not using 10% fragrance load, start with that. In the above example, a 6% fragrance load candle will cover 127.5 square feet. The same size candle with 10% fragrance load will cover 212.5 square feet. That’s a big difference.

If you’re already at 10%, then you need to use a larger candle container for your space.

If you don’t want to use a large candle container, then you need to use multiple candles to fill your space (and instruct your customers to do the same).

If your candle is sufficiently sized but still has a weak hot throw, you need to look at your melt pool (see below).

What's the science behind it?:

If you take a bucket that’s filled a few inches deep with water and dump it into a bathtub, it’s not going to create a bucket-shaped pool of water a few inches deep: it’s going to spread out and you’ll have a bathtub-shaped puddle that’s very shallow. Fragrance behaves the same way: it spreads to fill the available space. It’s just an invisible gas instead of a liquid. So if you take a candle that will strongly fill a bathroom and light it in your living room, it’s not going to make a “bathroom-sized” area around your candle smell strongly. It will make your “living room-sized” area smell very faintly.

Is your melt pool hot enough?

How to test for it:

Light your candle, let it burn for about two hours. Does your melt pool extend to the edges of your container? If not, your melt pool is definitely not hot enough. If it does extend to the edge of the container, get out your thermometer and measure the temperature at the edge of the container. Is it less than 145F/63C? Then your melt pool isn’t hot enough.

How to fix it:

Use a larger wick. Easier said than done. Chances are you don’t have a ton of different wicks on hand to experiment with, so start with this: take two of your existing wicks, dip them in liquid wax and twist them together to make an uber-wick, and test that in your candle. This is not a permanent solution. If you’re happy with the “uber-wick” now you have the unenviable task of finding an ideal wick size. Here’s a checklist to determine what size you should try next.

• If your melt pool doesn’t extend to the edges of the container, you are probably at least three sizes underwicked.
• If your melt pool is 135F-145F, increase by one size.
• If your melt pool is 125F-135F, increase by two sizes.
• If your melt pool is 115-125F, increase by three sizes.
• If your melt pool is 105-115F, that’s lower than the melting point for most waxes. Make sure you’re measuring correctly.

If you’re approaching the upper end of the available wick sizes, it’s probably better to use two wicks. Take the desired wick size, and cut it in half, (rounding up). Then increase one size, and that should be your starting point for double-wicking. To triple-wick, divide the size by three (this time rounding down) and then increase by one. I generally suggest buying smaller wicks because they offer you the flexibility to double-wick, giving you a larger range of containers you can work with.

If you’re still not happy with the hot throw, then you need to look at your fragrance oil.

What’s the science behind it?

Let’s start with this, and I’m going to repeat it multiple times: it is better to be over-wicked than under-wicked.

It is better to be over-wicked than under-wicked.

It is better to be over-wicked than under-wicked.

IT IS BETTER TO BE OVER-WICKED THAN UNDER-WICKED

Got it? Good.

If your melt pool does not reach the edge of your candle, you are under-wicked. Hard stop. If your wax is not warm enough, it will not release fragrance. And unmelted wax is definitely not warm enough. You could have a candle that’s two feet wide, but if only two inches of that wax is melted, it’s not going to smell any stronger than a candle that’s two inches wide.

The smell produced by a candle is the result of your fragrance oil evaporating off of the top of your melt pool. And just like how water evaporates faster when it’s hotter, your fragrance will evaporate faster when the melt pool is hotter. This is a good thing. You want your fragrance to evaporate, because that is what makes your room smell like fragrance instead of quarantine sadness. The alternative to your fragrance evaporating is your fragrance being consumed as fuel by your wick.

You want your melt pool to be as hot as possible without making your container dangerously hot to the touch. Practically speaking, this comes out to a temperature of around 150F at the edges of the container. A lot of factors go into how hot your melt pool is, first and foremost being the size of your wick. But I want to talk a bit about some of the other factors, because they’re all very much intertwined with each other.

Other than the size of your wick, your flame’s strength is primarily dependent on the amount of liquid fuel that’s available, which in turn is primarily impacted by the melting point of your wax, which itself is influenced by two main factors: what type of wax you use and how much fragrance oil you use.

Soy wax tends to have a lower melting point than paraffin wax. And the more fragrance oil you use (which is liquid at room temperature, unlike wax), the lower the melting point of your wax. A lower melting point is a double-edged sword. A lower melting point means that a smaller wick can melt more wax and get up to a full strength flame faster. But just because wax is liquid doesn’t mean that it’s hot enough to produce a strong hot throw. That liquid still needs to get **hot** before it can have a “hot throw”.

This is the big reason why soy wax traditionally has a "worse hot throw" than paraffin. Paraffin has a higher melting point, which means that by the time it’s fully liquid, it’s already about 10-15F hotter than a newly-liquified puddle of soy wax. Furthermore, it requires a larger flame to even reach that point in the first place. So the combination of these two factors results in a melt pool that tends to be much warmer than a comparable melt pool of soy wax.

Is it possible to “over-wick” your candle? Yes, but most people’s definition of “overwicked” is flat out wrong. The true symptom of an over-wicked candle is a container that is dangerously hot to the touch. The symptoms that most people tend to claim are due to “overwicking” are either completely irrelevant (like a melt pool that’s ‘too deep’), purely subjective (like a flame that’s ‘too large’), or the result of something else entirely (like mushrooming or sooting).

If any of these things happen before the melt pool reaches the edges of your container, then that isn’t a problem caused by over-wicking. When the melt pool is only an inch wide, it doesn’t matter if you have a two inch container or a ten inch container. Your wick isn’t psychic, it doesn’t know how large your container is. All that matters to it is how much liquid wax is available, and the size of the container doesn’t start to impact that until the melt pool reaches the edges of that container. Most cosmetic issues are caused by a wick that’s too long, or using a wick type inappropriate for your wax.

Is your fragrance oil simply not strong?

How to test for it:

Take whatever you use to melt wax and fill it about 1/2" deep worth of pure FO. Then heat it to around 150F and hold it there for an hour. Smell your room: this is the most possible strength you will ever get out of your fragrance oil from a candle.

How to fix it:

If you're not satisfied with it, you need to find a new FO. If you are really, really, really in love with the fragrance, you can juice things up by adding high quality essential oil [EO], or aromachemicals [AC]. Start with 9% fragrance oil and 1% essential oil / aromachemicals, and increase from there. How do you know if an EO is high quality? Does your vendor provide a GC/MS or COA to prove the purity and authenticity of their batches of EO? If not, then find one who does. Oh, and another way you’ll know it’s high quality: lots of them are painfully expensive! Here’s a quick crash course in some good inexpensive essential oils that mix well with fragrance oils:

• [EO] Any citrus essential oil (Citrus): in large quantities, citrus EO can be tricky in candles, but at the suggested amounts (2% or less of your total candle weight, 20% or less of your fragrance), you should be fine. Citrus is dirt cheap to extract, and it’s extremely distinct.
• [EO] Amyris (Sandalwood): Amyris is inexpensive, performs well in candles, and smells reasonably close to sandalwood.
• [EO] Cedarwood (Smoky): It smells like a lumberyard, or, as my five-year-old daughter says, “Home Depot”.
• [EO] Lavender (Lavender): Lavender is just a popular smell in general, and the essential oil gives a reasonable amount of “bang for the buck”
• [EO] Clove (Fall & Christmas): Almost entirely Eugenol, which is used to some degree in almost every fall or Christmas scent, being a component of cinnamon, clove, nutmeg, basil, allspice, star anise and others. Basically the entire pumpkin spice bouquet.
• [EO] Eucalyptus (Spicy, Woody, Minty): At high concentrations, it smells like Vick’s Vapo-Rub but in smaller concentrations, it gives that characteristic spicy note to wood fragrances.
• [EO] Patchouli (Earthy): Another one that can be a bit overwhelming at high concentrations, but at low concentrations it lends an earthy, woody, vaguely musky smokiness.
• [EO] Petitgrain (Grassy, Fruity): Extracted from the leaves and wood of the bitter orange tree, it gives an earthy, organic fruity smell without being too distinct.
• [AC] Ethyl Vanillin (Vanilla): It’s cheap and can boost the vanilla smell considerably.
• [AC] Aldehyde C-14 (Peach), C-16 (Strawberry), C-18 (Coconut), C-20 (Raspberry): These are all very one-note, but they’re effective at their respective flavors.
• [AC] Ethyl Butyrate (Sweet Fruity): Be careful as this is definitely more of a synthetic “candy” fruity smell than a natural fruity smell. But if you’re looking for that, this is the chemical for you.
• [AC (Strong)] Hexanal (Apple, Grassy): A little bit goes a LONG way, but this provide a very "natural" smell to your apple and grassy scents
• [AC (Strong)] Rum Ether (Woody, Smoky): This smells like the inside of a whiskey barrel. Very strong.
• [AC (Strong)] Dihydromyrcenol (Soapy, Perfumey - Floral): This is what gives Bath and Body Works candles that major scent bomb. It’s extremely fragrant and extremely distinctive. When you smell it, you’ll recognize it immediately.
• [AC (Strong)] Ultrazur (Soapy, Perfumey - Citrus): This is another one of those Bath and Body Works scent bomb type chemicals. Also extremely fragrant, but in more of a citrusy, oceany, fresh sort of way vs. the floral smell of Dihydromyrcenol.
• [AC (Strong)] Amber Xtreme (Woody, Amber): This will knock your socks off with an explosion of woody amber smell.

I plan on writing a larger guide on how to inexpensively use EO and AC to improve your candles, but this is a good inexpensive starter guide. Also - there are some notable exclusions from this list mainly based on cost.

What’s the science behind it?

So let’s just talk a little bit about what you’re actually smelling when you take a whiff of a fragrance oil. You’re smelling tiny little chemicals that have escaped whatever container happens to be holding them, and waft their way from the air into your nostrils. These chemicals are synthesized somewhere, whether it’s done in a lab or in the miraculous biological factory of nature.

So let’s consider Cinnamaldehyde, the primary molecule responsible for the “cinnamon” smell. A single cinnamon stick contains about 100mg of Cinnamaldehyde, which exists as a liquid at room temperature. And every molecule of which is bouncing around on a microscopic scale, desperate to escape the boring confines of its liquid state and vaporize into the surrounding atmosphere.

The degree to which the molecule is desperate to escape is quantified in a property called “vapor pressure”. These molecules, like air inside of a balloon, are putting pressure on the forces that keep them nice and contained in liquid form. The air around exerts a certain amount of pressure on, well, everything. This “atmospheric pressure” is just a little shy of 15 pounds per square inch, and is one of the primary forces fighting against the “vapor pressure” of a molecule.

Fun fact: when liquid is released into outer space (where there is no atmospheric pressure), it almost immediately boils away due to the complete lack of pressure holding it together. The tiny, diffuse vapor particles then almost immediately freeze due to the incredibly cold temperature.

Now, pressure, as you might remember from science class, increases with temperature. It’s very easy to increase the temperature of a small quantity of liquid, and insanely difficult to increase the temperature of the entire atmosphere (although we as humans appear to be trying our best). As such, the “atmospheric pressure” tends to remain fairly constant at ~15 pounds per square inch, whereas the “vapor pressure” of a liquid increases significantly as the temperature goes up. Once the temperature gets hot enough that the “vapor pressure” exceeds the “atmospheric pressure”, that’s what we call the boiling point.

At the boiling point, any molecule in the liquid can spontaneously turn into gas (which is the bubbles you see when something boils). But temperature (and therefore pressure) isn’t an all-or-nothing thing. Temperature is a distribution, an average. At a microscopic level, some molecules are cooler than others, some are hotter. So even at boiling point, some individual molecules still aren’t exerting enough pressure to escape, which is one of the reasons water doesn’t instantly boil away once it hits boiling point.

Similarly, even at room temperature, random individual molecules might just happen to be hot enough that they exert sufficient pressure to escape. But, if this random molecule is smack dab in the middle of the mixture, it almost definitely will randomly cool back down by the time it reaches the surface. This is why a puddle of water evaporates much faster than the same quantity of water in a glass: the more surface area, the faster the journey, and the easier it is for a molecule to exert enough pressure for long enough to escape.

Now, just like a puddle of water evaporating, there’s a finite number of fragrant molecules in a mixture and once they’ve evaporated, they’re gone. So let’s look back at our cinnamon stick, the one with about 100mg of Cinnamaldehyde lurking within it. Every time you take a whiff of a cinnamon stick, those are little bits of Cinnamaldehyde that have turned into vapor, and made their way into your kitchen, the air, and most importantly, your nostrils. And those little bits are never going to return back to that stick.

But since it’s a stick, since it’s solid and there’s not much surface area, there really aren’t that many opportunities for those little molecules of Cinnamaldehyde to escape. A small pinch of cinnamon powder is going to smell as potent (if not moreso) than a cinnamon stick that weighs twenty times as much, because there’s so much more exposed surface area. But on the flip side, that small pinch of cinnamon powder is going to lose its strength much faster.

This can be a good thing or a bad thing, depending on what you’re trying to accomplish. If you want to make a room smell like cinnamon, a cinnamon stick isn’t going to help you. But if you’re a chef, you want to keep all that precious Cinnamaldehyde locked up until the exact moment you’re ready to use it. Which is why chefs try to keep their spices in whole form rather than in powder. Powdered spices are to whole spices the same way that a puddle of water is to a glass of water.

But take that powdered cinnamon, mix it into a batter and pop it into the oven, and you get a different experience entirely. Your kitchen fills with the delightful aroma of baked goods: pressure increases with temperature, and at the hot temperatures of an oven, the molecules of Cinnamaldehyde are quite volatile, escaping into the surrounding air with ease.

But it’s not enough that a molecule vaporizes and escapes into the air and makes its way to your nose. (And this is where the objective science can only take us so far). Sure, we can measure the vapor pressure and molecular weight of different molecules. But the molecule needs to actually smell like something. Water, for example, is relatively volatile and has a fairly low molecular weight, but it smells like, well, water.

So first, let’s address the gardenia-scented elephant in the room: essential oils.

If you’re a beginner, don’t bother. Most of what you read on the internet about essential oils involves thoroughly questionable advice like “use 30 drops of essential oil for an eight ounce candle”. Thirty drops of essential oil is roughly 1.5 mL, which comes out to about 0.5% fragrance load. In other words: a recipe for utter disappointment.

Essential oils absolutely have a place. But good quality essential oils are insanely expensive and are absolutely not economical whatsoever. The corollary to this is that essential oils which aren’t insanely expensive are low quality. Of course, “insanely expensive” is relative, but we’re talking somewhere around $30 to $50 per ounce on the low end. You’ll never find a high quality essential oil for cheap, but you will find crappy essential oils that are expensive.

So, caveat emptor.

Fragrance oils, on the other hand, tend to be composed mostly of inexpensive synthetic aromachemicals. There’s nothing wrong with synthetics, and there’s nothing wrong with inexpensive. Unlike essential oils, there’s no such thing as a “low quality aromachemical”. A chemical is a chemical is a chemical. They’re manufactured in massive quantities, and they cost what they cost.

Some aromachemicals are dirt cheap. And some are really dirt cheap. It just so happens that a lot of the ones in the latter category don’t really smell like much. Benzyl benzoate is one example. It smells sorta kinda like almonds, but mostly it smells like nothing. And you can buy a gallon of it for like $20. It’s also a great solvent and a fixative, so it’s a really popular “filler” ingredient in fragrance oils. So if you’ve got a fragrance oil that’s 80% Benzyl Benzoate… It’s going to smell like 80% nothing.

This is why if you’re struggling with the strength of your candle, it’s crucial to test the fragrance by itself to see if you’ve just got a fundamental issue with a weak formulation. Now - this is where essential oils can come in handy. So, say you’ve got a fragrance oil that you love to death but it’s just not strong enough. You can juice it up with a little bit of high quality essential oil. Alternately, you can also use essential oils to put your own spin on existing fragrance oils. But again - don’t use cheap, low-quality essential oils.