A fire transfers heat through all three mechanisms: conduction, convection, and radiation. No single label covers it. That said, radiation is the dominant form of heat transfer in most fires, accounting for roughly 90% of the energy reaching nearby surfaces before flames arrive. Once flames are directly overhead or passing through, convection surges to contribute about half the total energy.
How Radiation Works in a Fire
Radiation is the heat you feel on your face and hands when you sit near a campfire. It travels as electromagnetic waves, primarily in the infrared spectrum, and doesn’t need air or any physical contact to reach you. This is the same basic mechanism that carries warmth from the sun to your skin.
The visible glow of a fire is itself a form of radiation. Tiny soot particles produced during combustion get extremely hot and emit what physicists call blackbody radiation. Those glowing particles are what give a wood fire its characteristic reddish-orange-yellow color. A hotter fire shifts the color toward yellow and white; a cooler or dying fire glows a deeper red. When a flame burns with plenty of oxygen and produces very little soot (like a blue gas flame), it actually radiates far less visible light, even though the gas temperature can be higher.
Research on wildland fires measured the energy arriving at sensors as flames approached. Before the flames reached the sensor location, radiant energy made up approximately 90% of the total heat transfer. Radiation is especially dominant at a distance because it can travel through air without being carried by it. This is why you can feel a large bonfire from 20 feet away, even if the wind is blowing in a completely different direction.
How Convection Works in a Fire
Convection is heat carried by moving air or gas. When a fire heats the air around it, that air expands, becomes less dense, and rises. Cooler air rushes in to replace it, creating the upward draft you see pulling sparks and smoke skyward. If you hold your hand above a fire (not recommended), the heat you feel is almost entirely convective, because the rising column of superheated gas is flowing directly past your skin.
Convection plays a much bigger role once flames are directly present. Measurements from wildland fire research showed that during and immediately after ignition, convective heating jumped dramatically, accounting for close to 50% of total energy transfer as flames passed through the sensor area. This makes sense: once you’re inside the flame zone, hot gases are actively flowing over surfaces rather than just radiating from a distance.
Wind-driven convection is also a major factor in how fires spread. A strong wind pushes hot gases ahead of the flame front, preheating unburned fuel. On steep slopes, rising hot air naturally flows uphill along the terrain, which is one reason wildfires climb hills so quickly.
How Conduction Works in a Fire
Conduction is heat moving through direct physical contact, the way a metal poker gets hot when one end sits in the flames. It requires molecules to be touching and passing energy along to their neighbors, so it only happens within solid objects or between surfaces pressed together.
In the context of a campfire or house fire, conduction is the least significant of the three mechanisms for transferring heat to you. Air is a poor conductor, so heat doesn’t travel well through it by conduction alone. Where conduction does matter is inside the fuel itself. Heat conducts through a log from the burning exterior inward, raising the internal temperature until deeper layers begin to decompose and release flammable gases. The thermal conductivity of the wood directly affects how fast this happens: denser woods conduct heat inward more quickly, which changes how rapidly the material breaks down and feeds the fire.
Conduction is also the reason fires can spread through structural materials. A steel beam heated on one end will conduct that energy along its length, potentially igniting materials in contact with the far end. In bulk storage of wood chips or biomass, internal heat generated by slow chemical reactions can build up if conduction doesn’t dissipate it to the surface fast enough, sometimes leading to spontaneous ignition.
Why the Balance Shifts With Distance
The mix of conduction, convection, and radiation you experience from a fire depends heavily on where you are relative to the flames.
- Far from the fire: Radiation dominates. It’s the only mechanism that doesn’t need moving air or physical contact. At a distance, convective currents rise upward rather than reaching you horizontally, and conduction through air is negligible.
- Directly above the fire: Convection dominates. The column of rising hot gas carries enormous amounts of energy straight up. This is why the area directly above a fire is far more dangerous than the area beside it at the same distance.
- In contact with burning material: Conduction becomes relevant. Touching a hot coal or heated metal transfers energy directly through contact, which is why burns from touching are typically deeper and more severe than burns from radiant exposure at the same temperature.
Fire Size Changes the Equation
As fires get larger, radiation becomes increasingly dominant. Fire safety research has identified thermal radiation as the most important heat transfer mechanism in medium to large fires. A small candle flame loses most of its heat through convection (the hot air simply rises away), but a large structure fire or wildland fire radiates enough energy to ignite buildings across a street or trees dozens of meters ahead of the flame front.
This scaling effect happens because radiant energy output increases with the fourth power of temperature, following the Stefan-Boltzmann law. In practical terms, doubling the temperature of a burning surface doesn’t double the radiation: it increases it roughly sixteenfold. Large fires with tall, hot flame fronts therefore radiate disproportionately more energy than small ones, which is a key reason why wildfires become exponentially harder to control as they grow.