Thermal FAQ’s


How is heat transferred?

Although heat can be transferred in a variety of ways, the three most common ways are:

  • Conduction
  • Convection
  • Radiation

In Conduction, heat travels through a solid material such as ceiling tiles, floor tiles, and walls.

In Convection, heat travels through a fluidic medium, such as air or water. When air is heated it expands, becoming less dense, and therefore rises as far as it can go (in an oven, in a room, or in the open air). As the air rises away from the heating source, it gradually cools, condenses, and sinks closer to the heating unit again, and the process is repeated. The hotter air (or water) transfers energy to the cooler air (or water) as it circulates.

With Radiation, heat is transferred from a hot body to a colder body through the use of electromagnetic waves. There is no need for the hot body to contact the cooler body for the heat to be transferred.

Terms can sometimes be misused. For example, despite its name, a radiator transfers most of its heat into a room by convection, not radiation.

Reflective insulation in the attic or crawl spaces reflects 95% of that heat back up toward the roof, and the insulation material below the reflective barrier (foil) lets very little heat continue downwards (or to put it technically, emits very little heat).

What is an R-value?

The R value, or thermal resistance of a material, expresses the ability of a particular thickness of that material to resist heat flow. A higher R-value represents a greater ability to resist heat transfer.

What is the difference between a Material R-value and a Total R-value?

A Material R-value or ‘insulation value’ is simply the R-value of the insulation material itself. A Material R-value does not consider any other elements of construction.

A Total R-value or System Value takes into account all elements of a wall, roof, or floor system including insulation, air gaps, air films, cladding types etc.

What does Section J refer to?

Section J refers to a part of the National Construction Code (NCC) relating to energy efficiency. The aim of Section J is to ensure all new buildings are built in an energy efficient manner to reduce levels of greenhouse gas emissions. All new commercial building projects are required to demonstrate compliance to Section J (generally at construction certificate stage) to verify the building works complies with the provisions outlined in the NCC.

Fletcher Insulation uses Section J to complete thermal calculations, which are provided to Architects and Energy Consultants. Thermal calculations recommend insulation products that allow you to satisfy the designated energy efficiency requirements for a given building.

What is a thermal calculation?

Thermal calculations are used to obtain the thermal resistance for wall, floor and roof systems. These calculations take into account such elements as:

  • Class of building;
  • Climate zone; and
  • Construction elements.
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