Touch a metal spoon left in boiling water and you feel heat within seconds. Hold your hand above the pot and you feel heat rising. Stand across the kitchen and you still feel warmth on your face. Three different mechanisms, one pot, all at the same time.
The Short Answer
The three types of heat transfer are conduction, convection, and radiation. Conduction moves energy through direct contact between particles. Convection moves energy by physically carrying hot fluid from one place to another. Radiation moves energy as electromagnetic waves and needs no medium at all.
Every real situation involves some mix. A house loses heat through all three simultaneously, which is why insulation alone never solves the whole problem.
Conduction
In a solid, atoms are locked in a lattice. Heat them at one end and they vibrate harder, jostling their neighbors, which jostle theirs. Energy travels through the material without the material itself moving. In metals, free electrons carry energy much faster than vibrations, which is why metals conduct so well.
The rate depends on the material’s thermal conductivity, the temperature difference, the cross-sectional area, and the thickness. Double the thickness and you halve the heat flow. That is the entire logic behind a sweater.
| Material | Thermal conductivity (W/m·K) |
|---|---|
| Copper | ~400 |
| Aluminum | ~235 |
| Steel | ~50 |
| Glass | ~1.0 |
| Water | 0.6 |
| Wood | 0.1 to 0.2 |
| Air | 0.026 |
| Aerogel | 0.015 |
Air is a terrible conductor, which is why foam insulation works: it is mostly trapped air, and trapped air cannot convect. Down jackets and wool sweaters use the same trick.
Convection
Heat a fluid from below and it expands, becomes less dense, and rises. Cooler fluid sinks to replace it. That circulation carries enormous amounts of energy, and it is usually far more effective than conduction in liquids and gases.
Natural convection is driven by buoyancy alone — a radiator heating a room, a sea breeze forming as land warms faster than water. Forced convection uses a fan or pump, which is why a computer has case fans and a car has a water pump.
The same mechanism runs the planet. Hot air rises at the equator, moves poleward, cools, and sinks. Ocean currents do the same with water, moving roughly 30% of the heat from the tropics toward the poles.
Radiation
Every object above absolute zero emits electromagnetic radiation, and the amount scales with the fourth power of temperature (the Stefan-Boltzmann law). At everyday temperatures the emission is infrared, invisible to your eyes but detectable as warmth on your skin.
Radiation is the only type that works through a vacuum. That is how the Sun’s energy reaches Earth across 93 million miles of empty space, and how a thermos bottle keeps coffee hot — the vacuum between the walls kills conduction and convection, and the silvered surfaces reflect radiation back.
Unlike conduction and convection, radiation does not need matter at all. It is also the reason you feel cold in a room at 65°F even though the air is not that cold: your body is radiating heat to the cold walls faster than they radiate it back.
All Three at Once
| Situation | Conduction | Convection | Radiation |
|---|---|---|---|
| Boiling pot on a stove | Burner to pot, pot to handle | Water circulating, steam rising | Hot pot glowing, infrared |
| Heated room | Through walls | Radiator air currents | Warm walls to furniture |
| Campfire | Log to ground | Smoke and hot air rising | Most of the heat you feel |
| Earth’s climate | Ground to air | Atmosphere and oceans | Sunlight in, infrared out |
That is why the three types of heat transfer are taught together rather than separately: in any real system they run at once and trade off against each other, and fixing one usually changes the balance of the other two.
Why Metal Feels Cold
A metal table and a wooden table in the same room are at the same temperature. The metal feels colder because it conducts heat away from your hand about 2,000 times faster. Your skin is not measuring temperature — it is measuring heat flow.
This is also why a 60°F tile floor feels colder than a 60°F rug. Same temperature, different conductivity, different sensation.
The Greenhouse Connection
Earth receives visible light from the Sun and re-emits it as infrared. Greenhouse gases like CO2 and water vapor are transparent to visible light but absorb infrared, then re-radiate it in all directions, including back down.
That is radiation doing the work, not convection. The atmosphere does not “trap” heat the way a blanket does; it changes the altitude at which Earth’s radiation escapes to space. Raise that altitude and the surface has to warm to maintain balance.
Keep Exploring
- What causes global warming? — the radiation balance in detail
- How do ocean currents work? — convection on a planetary scale
- How does a microwave work? — heating by radiation, not conduction
