The specifications on a heater's hearth is quite strict as it's the protective barrier between the unit and your flooring. This has been specified in AS/NZS 2918:2001 3.3.2 outlining the requirements for a hearths Thermal Resistivity (Wm²/K).

To calculate the Thermal Resistivity of a material we shall use the formula:

R=depth / λ

R=Thermal Resistivity ((Wm²)/K)

This is a materials thermal resistance which prevents heat transfer through a material.

λ = Thermal Conductivity of the Material(W/mK)

This is the property of a material that indicates its ability to conduct heat.


Below is some common material that are used and their Thermal Conductivity:

VillaBoard λ=0.23 W/mK

Hardie Panel λ=0.5 W/mK

Glass λ=1.05 W/mK

Sandstone λ=1.7W/mK

For the Vogue Navara, it has been specified that the Thermal Resistivity be 0.0136 Wm²/K.
Using the Thermal Resistivity formula above we can determine the minimum thickness a material is required to be to meet the requirements of the heater.

An example of this can be seen below.

Depth= R x λ

For CFS λ=0.23 W/mK

Depth= 0.0136 / 0.23

Depth= 0.059m

Depth=4.5mm

Therefore, when using a VillaBoard as a Thermal Barrier in your hearth for a Vogue Navara, it is required that a minimum of 4.5mm of Villaboard be used.

Therefore, when using a Glass as a Thermal Barrier in your hearth for a Vogue Navara, it is required that a minimum of 43mm of Glass be used.


If you have any questions or concerns, please feel free to contact us regarding a heater or material. Give us a call on 3375 1464.