Methods of heat transfer

Heat can be transferred by conduction, convection or radiation, or due to a combination of those three ways. Heat always moves from the warmest areas to the coldest ones, seeking for a balance. It is known as zeroth law of thermodynamics. The bigger the temperature difference is, the fastest heat will flow to the coldest area.



Conduction is heat transfer by means of molecular agitation within a material, may it be solid, liquid or gas material. Heat transfer to be completed by conduction implies a physical contact between particles and a certain temperature difference. Thermal conductivity is the measure of the speed of the heat transfer when heat flow rods from a particle to another. Heat flow rate through a specific material will be determined by temperature difference and the material’s thermal conductivity.


Convective heat transfer, often referred to simply as convection, is the transfer of heat from one place to another by the movement of fluids, either air (or gas) or a heated liquid. Heat flow rate will vary depending on the moving fluid (gas/liquid) temperature and its flow. The most relevant convections in building thermal balance are losses (or gains) by ventilation and by infiltrations. Generally, air conditioning works only by convection.


Heat energy is transferred through light, as infrared light or other type of electromagnetic waves. This energy arises from a hot body and it can only be freely transferred by completely see-through means. Atmosphere, glass and translucent materials allow a relevant radiant heat to go through them. This heat can be absorbed when it impinges on a surface. Both solar gains and internal gains are basically heat radiations. Ideal heating system is through radiation or a combination between radiation and convection.

Thermal conditioning in buildings is based on radiation and convection

In practice, heat transfer in houses is the result of the already three mentioned methods, but the most relevant transmission way is conduction through the blind coating in the building.

Heat transfer in buildings

What is a thermal insulator material?

A thermal insulation material is a material used in building and industry, characterized by its high thermal resistance. It sets a barrier to avoid heat transfer between two means which naturally would tend to balance its temperatures.

In general all those materials offer resistance to heat transfer, but to be considered as a thermal insulation material its thermal conductivity coefficient (λ) is to be under 0.10 W/m²·K measured at 23°C.

Cork, specific thermal insulation material

Thermal insulation materials with thermal conductivity of <0,08 W/mC are called specific thermal insulation materials. VIPEQ F08 has a thermal conductivity of 0,058 W/mC.

Thermal insulators’ functions

Functions and characteristics that a thermal insulation material must fulfil:

  • It saves in energy use because it enhances the thermal resistance of the building envelope.
  • It improves thermal comfort.

Insulation advantages

Incorporating thermal insulation in buildings contributes to:

An energetic and economic saving

Including thermal insulation reduces heat or cold losses (winter/summer) within the building. Therefore, the energy required to heat or chill rooms will be reduced and it will mean a reduction on the energy bill.

Reduce emissions

A thermally well insulated house contributes to reducing energy consumption and, therefore, to reduce green-house effect emissions, mainly CO2, which are generated by gas boilers, and carbon and petrol derivatives.

An improvement in comfort

It helps the user maintain a comfortable temperature inside the house.

It avoids mould formation

Eliminating condensations and indoor moistures which generate mould appearance.

Other advantages

An improvement in acoustic insulation in the building and, in some cases, in protection against the fire.

Thermal conductivity scale λ (W/mK)

Thermal conductivity scale

Properties and thermal insulators characteristics

There are plenty of insulation materials on the market, but with differences among them. Their main characteristic is the thermal conductivity (λ) which differentiate one insulation material from another.

Spanish Technical Building Code DB HE-1 states that products for walls and blind spaces on façades are defined by the following hygrometric conditions:

Thermal conductivity

Thermal conductivity is a physical property which measures the insulation capacity of a material. The lower the rate, the more ability to reduce the rate of heat flow. It is an inherent property of the material, it does not have a fix value, because it depends on different factors such as temperature, density, humidity and the ageing process of the material.

Water vapour resistance factor μ.

It has to be taken into account, especially in those insulation projects which aim to preserve a cold surface. If the insulation enables the air humidity to be in contact with the cold surface, there will be condensation and it will make the insulation material wet, generating insulation capacity losses, wet surfaces and even hygienical problems and moulds.

Density ρ (kg/m3)

The volumetric mass density of a substance is its mass per unit volume.

Specific heat cp (J/kg.K)

It is the energy which results in an increase in temperature and proceeds to the transformation of other energies.