Conduction vs Convection vs Radiation
Heat moves in three ways. Conduction passes energy from particle to particle through direct contact. Convection carries energy with a moving liquid or gas. Radiation sends energy as electromagnetic waves (mostly infrared), which need no material at all and can cross empty space.
Last reviewed on 2026-10-03.
Quick Comparison
| Aspect | Conduction | Convection | Radiation |
|---|---|---|---|
| How heat moves | Collisions between neighbouring particles (and free electrons in metals) | Bulk movement of a warm fluid carrying energy with it | Electromagnetic waves emitted by every object above absolute zero |
| Medium needed | Yes — solid, liquid or gas (best in solids) | Yes — liquids and gases only | No — works through a vacuum |
| Does matter move? | No, only energy passes along | Yes, the fluid itself flows | No matter needed at all |
| Key equation | Fourier's law: Q/t = k·A·ΔT / d | Newton's law of cooling: Q/t = h·A·ΔT | Stefan–Boltzmann law: P = ε·σ·A·T⁴ |
| Everyday example | A metal spoon getting hot in soup | Warm air rising from a radiator | Feeling the Sun's warmth or a campfire's glow |
| How to reduce it | Insulators with trapped air (foam, wool) | Block air flow (draught-proofing, double glazing gap) | Shiny or reflective surfaces (foil blankets, low-E glass) |
Key Differences
1. Conduction: Heat Through Contact
Conduction happens when faster-vibrating particles bump into slower neighbours and pass on some of their kinetic energy. Nothing flows from place to place — the energy is handed along. In metals, free electrons carry much of the energy, which is why metals feel cold to the touch and heat up quickly.
How fast heat conducts depends on the material's thermal conductivity k. Approximate values at room temperature: copper about 400 W/(m·K), steel about 15–50 W/(m·K), glass about 1 W/(m·K), water about 0.6 W/(m·K), and still air about 0.026 W/(m·K). That huge range is why a metal pan handle burns while a wooden one does not.
2. Convection: Heat Carried by a Moving Fluid
Convection needs a fluid (a liquid or a gas). When part of the fluid is heated it expands, becomes less dense and rises; cooler, denser fluid sinks to replace it, forming a convection current. This is natural (free) convection. When a fan or pump pushes the fluid, it is forced convection, which moves heat much faster.
Convection drives sea breezes, ocean currents, weather systems and the circulation of the Earth's mantle. It cannot happen in a solid because the particles cannot flow, and natural convection depends on gravity — on the International Space Station a candle flame forms a sphere because hot gases do not rise.
3. Radiation: Heat as Electromagnetic Waves
Thermal radiation is energy emitted as electromagnetic waves. Every object above absolute zero radiates; at everyday temperatures the waves are mostly infrared, which we feel as warmth but cannot see. Very hot objects (a stove element, the Sun) also glow visibly.
Because radiation needs no medium, it is the only way heat crosses the vacuum of space — it is how sunlight warms the Earth across about 150 million km. The power radiated rises with the fourth power of absolute temperature (Stefan–Boltzmann law), so doubling an object's absolute temperature multiplies its radiated power by 16. Dark, matte surfaces absorb and emit radiation well; shiny surfaces reflect it.
4. How the Three Work Together
Real situations almost always involve more than one mode. In a pot of boiling water, the burner heats the pot base (radiation and conduction from the flame), heat conducts through the metal, and the water circulates by convection. Standing near the stove, you also feel radiation on your face.
A vacuum flask (thermos) is designed to block all three: the vacuum between its double walls stops conduction and convection, the silvered inner surfaces reflect radiation, and the stopper limits convection out of the top.
5. Which Is Fastest?
The question has no single answer. Radiation travels at the speed of light, but how much energy it delivers depends on temperature and surface properties. Convection usually moves heat through a room faster than conduction through still air, while conduction through a metal is very rapid compared with conduction through an insulator. Engineers compare the modes by calculating the heat-transfer rate for each in the specific situation.
Everyday Examples of Each
Conduction
- Touching a hot pan handle
- Ice cube melting in your hand
- A CPU heat sink drawing heat from the chip
- Cold floor tiles feeling colder than carpet
- Ironing clothes
Convection
- Boiling water rolling in a pot
- Radiator warming a room
- Sea and land breezes
- Convection (fan) ovens
- Hot-air balloons rising
Radiation
- Sunlight warming the Earth
- Heat felt from a campfire or toaster
- Infrared heat lamps
- Microwave and infrared cooking
- Thermal cameras detecting body heat
Example: All Three at a Campfire
Radiation warms your face and hands even though the air between you and the fire is cool. Convection carries hot air and smoke upward — which is why it is hottest directly above the flames. Conduction heats a metal skewer left in the fire until the handle end is too hot to hold.
Frequently Asked Questions
What are the 3 types of heat transfer?
Conduction (through direct contact between particles), convection (through the movement of a liquid or gas) and radiation (through electromagnetic waves, which need no medium).
Can heat travel through a vacuum?
Only by radiation. Conduction and convection both need matter, so in a vacuum such as outer space radiation is the only way heat can move. That is how the Sun heats the Earth.
Is boiling water conduction or convection?
Both. Heat conducts through the bottom of the pot into the water touching it, and then convection currents carry the heated water upward and spread the heat through the pot.
How does the Sun heat the Earth?
By radiation. Sunlight (visible light, infrared and ultraviolet) crosses about 150 million km of near-vacuum. Once it is absorbed, conduction and convection spread the heat through the ground, oceans and atmosphere.
What is the difference between conduction and convection in simple terms?
In conduction the material stays still and the heat is passed along it, like a relay. In convection the warm material itself moves and carries the heat with it. See convection vs conduction for a detailed comparison.