How Heat Is Transferred in Buildings

All heating systems rely on the same fundamental physical processes: radiation, convection and conduction.

What differs between systems is which mechanism dominates, how heat is distributed through a building, and how occupants perceive comfort as a result. Modern Australian and New Zealand buildings — characterised by high insulation levels, airtight construction and sensitive interior materials — respond very differently to these heat transfer mechanisms than older housing stock.

This document explains how heat is transferred within buildings, how each mechanism influences comfort and material behaviour, and why surface temperature and radiant balance have become critical performance factors in modern construction.

All heat transfer in buildings occurs through one or more of the following mechanisms:

Heat transfer through electromagnetic waves.

Radiant heat travels directly from warmer surfaces to cooler bodies without relying on air movement.

All radiant heating systems warm people and objects primarily through surface temperature, rather than by heating air. This is what distinguishes radiant heating from convective systems.

Some radiant systems — such as traditional hydronic underfloor heating and conventional electric cable systems — rely primarily on surface warmth created by heated water or resistive cables. These systems are radiant in effect, but they are not specifically designed to emit far-infrared energy. Other systems use materials engineered to emit heat predominantly within the far-infrared (FIR) range of the infrared spectrum. Far-infrared energy is the same form of heat experienced from sun-warmed surfaces and is also used in infrared wellness and therapeutic environments.

In building applications, this distinction matters because:

• all radiant floors warm through surface contact

• only some systems are designed for FIR emission

• FIR is a material and emission property, not a default characteristic of all underfloor heating

Examples of radiant heat sources in buildings include:

• sun-warmed floors and walls

• hydronic radiant floor systems

• electric cable radiant floor systems

• engineered radiant systems designed to operate within the far-infrared spectrum

Heat transfer through the movement of air or fluid.

Convection occurs when air is heated, becomes lighter, rises, and is replaced by cooler air, creating continuous circulation within a space.

In buildings, convection is the primary mechanism used by systems that heat air first, rather than surfaces.

Examples of convective heating include:

• ducted air heating systems

• fan heaters and split systems in heating mode

• radiators that warm surrounding air

• warm air rising from heaters and pooling near ceilings

Convection-based systems rely on:

• continuous air movement

• ongoing reheating of displaced air

• temperature stratification (warm air above, cooler air below)

In modern buildings, convection behaves differently than in older homes. Highly insulated and airtight construction reduces natural air leakage, which can:

• limit effective air circulation

• increase temperature stratification

• create uneven comfort between head and foot level

Convection can provide rapid air temperature changes, but it does not directly warm surfaces. As a result, occupants may still experience discomfort from cold floors or walls, even when the air temperature is elevated. This is why convective heating often requires higher air temperatures to achieve comfort compared to radiant-dominant systems.

Conduction occurs when heat moves from a warmer object or surface to a cooler one through physical touch.

In buildings, conduction governs how heat moves through construction layers, rather than through the air.

Examples of conduction heating and heat transfer include:

• warmth moving from an underfloor heating element into the screed or levelling compound

• heat travelling through tiles, stone or timber from the warm underside to the surface

• a warm floor transferring heat to bare feet on contact

• heat moving through concrete slabs, subfloors and structural elements

Conduction does not heat a room directly. Instead, it enables heat to move into surfaces, which may then warm occupants through radiation or air through convection.

In underfloor heating systems, conduction plays a critical role in:

• distributing heat evenly across the floor surface

• influencing warm-up time

• shaping surface temperature stability

• affecting how flooring materials respond to heat

Correct floor build-ups, material selection and layer thickness are therefore essential to ensure conduction supports stable radiant performance rather than creating localised hot spots or thermal stress.

Human thermal comfort is not determined by air temperature alone. Comfort is influenced by:

• mean radiant temperature

• surface temperatures of surrounding elements

• temperature stability

• air movement

• humidity
• skin receptors

A person standing in a room with warm surrounding surfaces will feel comfortable at a lower air temperature than in a room with cold surfaces and warm air.

This is why surface temperature matters.

Mean Radiant Temperature (MRT) is the weighted average temperature of surrounding surfaces.

In modern buildings:

• MRT often dominates comfort perception

• Small changes in surface temperature are strongly felt

• Cold floors or walls create discomfort even in warm air

Heating systems that raise MRT evenly can achieve comfort with less energy input.

Highly insulated, airtight buildings reduce heat loss and air leakage.

As a result:

• convective air movement becomes less effective

• surface temperature balance becomes more important

• small thermal imbalances are more noticeable

Radiant-dominant systems stabilise MRT and reduce reliance on air temperature elevation.

Modern flooring systems are sensitive to:

• rapid temperature change

• localised overheating

• uneven surface temperatures

Heating systems that distribute heat evenly across surfaces reduce:

• thermal stress

• adhesive fatigue

• dimensional movement

This makes surface stability a performance requirement, not a secondary consideration.

Modern construction amplifies the importance of radiation because:

• insulation reduces heat loss

• airtightness reduces convective exchange

• interior finishes retain heat

• occupants are closer to surface temperature effects

In these environments, radiant balance becomes the dominant comfort driver.

• Heat is transferred through radiation, convection and conduction

• Humans perceive comfort largely through surface temperature

• Mean radiant temperature strongly influences comfort

• Modern buildings amplify surface temperature effects

• Radiant-dominant heating stabilises comfort at lower air temperatures

• Surface temperature stability protects materials and finishes

SC-03 — Radiant vs Convective Heating Architectures

RE-02 — Surface Temperature, Comfort & Human Thermal Perception

DS-03 — Wattage Density, Spacing & Even Heat Distribution