How High Does The Heat From A Candle Go?

Intro

Candles have been used for centuries as a source of light and heat in homes and other indoor spaces. But how high does the heat actually rise from a burning candle flame? In this article, we’ll look at the factors that determine candle flame height, the maximum temperature a candle flame reaches, the methods of heat transfer from a candle, and how heat rises and spreads from the flame. We’ll also discuss some experiments that have measured candle heat, the impacts and uses of candle heat, and the limitations of candles as a heat source.

What Determines Candle Flame Height

There are a few key factors that determine how high the flame will rise above a candle.

One major factor is the length of the candle’s wick. Longer wicks tend to produce taller flames. This is because a longer wick can draw up more melted wax via capillary action, which provides more fuel for combustion at the tip. Shorter wicks cannot supply as much fuel, resulting in a lower flame height [1].

Another important determinant is the actual composition of the candle wax. Different types of waxes, such as paraffin, soy, or beeswax, have varying properties that affect flammability. Some wax blends contain more hydrocarbons and burn more readily, enabling a taller flame. Waxes with a higher melting point may also sustain a higher flame [2].

Air currents in the environment around the candle can also influence flame height. Drafts and breezes that pass through the flame can “bend” it or cause it to dance and rise higher before being blown out. Still air conditions usually result in a lower, steadier flame height.

Max Flame Temperature

The maximum temperature of a candle flame occurs at the tip of the inner blue cone, in an area known as the primary reaction zone.^[1] For standard paraffin wax candles, this temperature typically ranges from 1470–1700°C.^[1][2] This high heat is a result of the combustion reaction between vapors released from the melted wax and oxygen in the air.

What determines the max temperature of the flame? It depends largely on the type of wax used in the candle. Paraffin wax, one of the most common types, burns at temperatures around 1500°C. Beeswax, in comparison, burns cooler at around 1200°C due to a lower hydrocarbon content.^[3] Additives like stearin can increase the melting point of the wax and the resulting flame temperature.

Within the flame, temperatures gradually decrease further from the blue reaction zone. The inner orange-yellow zone may reach 1300°C and the outer flames around 1000°C.^[2] Understanding the high temperatures involved emphasizes the need for caution around open flames to avoid potential burns or fires.

^{[1] https://hypertextbook.com/facts/1999/JaneFishler.shtml
[2] https://en.wikipedia.org/wiki/Candle
[3] https://www.harlemcandlecompany.com/blogs/journal/how-hot-does-a-candle-get-how-to-avoid-getting-burned}

Heat Transfer Methods

There are three main ways that heat transfers from a candle flame into the surrounding environment: conduction, convection, and radiation.

Conduction is the transfer of heat through direct contact with the flame. Heat conducts along the wick to vaporize wax and up through the air surrounding the flame. According to research by Koppenhoefer, conduction plays only a minor role in heat transfer from a candle flame due to the lack of direct contact with most surfaces [1].

Convection occurs as hot gases rise from the flame. This transfer of heat via circulation or motion of fluids is a significant contributor to heating the area around a candle. Hot air rises from the flame, transferring thermal energy by convection. Cooler air then moves in to take its place, creating convective air currents [2].

Radiation transfers heat in the form of infrared waves directly from the flame to surrounding objects. Radiant heat spreads out in all directions and is able to travel through air or a vacuum without direct contact. This makes radiation a major method of heat transfer from a flame.

Convection Effects

Convection plays a major role in how heat from a candle flame transfers through the surrounding air. When a candle burns, it heats the air closest to the flame. As this air becomes hotter, it becomes less dense and rises above the flame. Cooler, denser air then moves in below to replace the rising hot air. This creates a continuous convection current, with hot air rising above the flame and cooler air moving in below [source 1]. This rising hot air transfers heat upward and outward from the flame through the process of convection.

The convection effect causes flame heat to rise above the candle, rather than spreading equally in all directions. It also allows heat to travel greater vertical distances from the flame as hot air continues to rise. For example, your hand held above a candle can feel noticeable heat convection currents a foot or two above the flame [source 2]. So convection enables the candle’s heat to impact objects considerably above it.

Radiant Heat Spread

The heat from a candle flame radiates outward in all directions in the form of infrared radiation. Infrared radiation, which we perceive as heat, can be felt within 1-2 feet of the candle flame. This radiant heat follows the inverse square law, meaning its intensity diminishes rapidly with distance from the source. At 12-24 inches from the flame, the infrared radiation becomes too weak to detect. However, radiant heatplays an important role right near the candle providing localized warmth. As noted in [this video](https://www.youtube.com/watch?v=U1DRykuO0uQ), you can feel the radiant heat on your hand by holding it 1-2 inches from the flame. The radiant heat component adds to the overall heat output making candles more effective for localized heating applications.

Conduction Limitations

Conduction through the air around a candle flame is very limited. Air is not a good conductor of heat. This is why a candle flame does not conduct much heat to the surrounding air until that air gets close enough to the flame to be heated through convection (see the Convection Effects section). As noted in the Analysis of Burning Candle paper, “The low thermal conductivity of air prevents rapid dissipation of heat away from the flame reaction zone” (source). The candle flame creates hot air and gases immediately around it, but conduction does not spread that heat very far or very quickly through the cooler surrounding air.

Experiment Results

Several experiments have measured the heat emitted by candle flames at different heights above the wick. One study by Ward’s Science used a thermocouple to take temperature readings at various points above a burning candle. They found that right at the tip of the inner flame core, temperatures reached around 1400°C. At 2.5 cm above the wick, temperatures were around 1000°C. At 5 cm above the wick, temperatures dropped to around 500°C. And at 7.5 cm, temperatures fell to just above 100°C (1).

Another experiment analyzed candle flame shapes and temperatures using video recording techniques. They found that candle flames are not symmetrical cones, but rather have complex shapes influenced by convection currents. The hottest part of the flame was consistently right above the wick, with temperatures rapidly dropping further away in all directions. Peak temperatures reached around 1300°C (2).

Overall, experiments show that candle flame heat is highly concentrated near the wick and drops off steeply with height above the candle. Just a few centimeters above the flame, heat is significantly reduced.

Sources:

(1) https://www.wardsci.com/www.wardsci.com/images/CandleFlameThrmocple.pdf

(2) https://www.sciencedirect.com/science/article/abs/pii/S1540748910001665

Impacts and Uses

Candles have been used for lighting, heating, and rituals for thousands of years. The height of the candle flame impacts how much light and heat is produced (Why is my Candle Flame so High? – The Sojourn Company). Taller flames generate more light to illuminate dark spaces. They also produce more heat that can be felt from a distance. In rituals, the height of the flame is believed to correlate with the intensity of the prayer or intention (Why is the height of the water different if the number …). A higher flame is thought to send more energy into the universe.

For lighting, the brightness of the flame is the priority. Candles designed for lighting purposes often have fuels and wicks engineered to achieve the maximum flame height while avoiding excessive smoking. This provides bright illumination without compromising safety.

For heating, flame height is adjusted to create the optimal level of radiant heat output. Too short and the heat is weak. Too tall and the flame becomes unstable and drips wax. There is a sweet spot flame height that maximizes heating efficiency.

For rituals, flame height carries meaning about the power of the candle. Shorter flames are used for gentle intentions, while taller flames are used for stronger requests. The tallest ritual candle flames represent the release of potent energy into the cosmos.

By considering how the candle will be used, manufacturers can design the right candle and wick to produce a flame height that aligns with the intended application.

Conclusion

In conclusion, candle heat dissipates by three heat transfer methods. While the maximum tip flame heat can reach about 1400°C, the flame spread height is determined by multiple factors like wick size, melted wax pool, and oxygen supply. Experiments show candle heat rises but quickly dissipates within a couple inches of the flame. This allows focused heat without spreading too high. Candles radiate heat in all directions but mainly upwards in the path of least resistance. This allows candles to provide gentle, soothing heat without getting too hot. The maximum candle flame height reaches around 12 inches high with standard household candles.