Radiant Vs Convection

Key differences: Radiant Vs convection heat


Radiant heat warms objects and surfaces without heating the air in between. Those objects warm up directly and radiate back.

Convection warms the air, which is a triple inefficiency. The air has to:

  • Warm up. Air absorbs heat poorly;
  • Travel (unforced convection of heat is always upwards to the ceiling or through doors and windows. Only forced convection – using a fan – convects heat horizontally );
  • Deliver the heat to something. Air transfers heat out poorly;

Degree for degree °C, radiant heat delivers 4x the heat transfer capability of convection.



Convection inefficiency diagram




  • Heat exchange has to occur twice (indirect heating of objects)
  • Air absorbs & retains heat poorly
  • Hot air rises and is prone to infiltration loss (draughts)
  • Air heats thermal mass poorly, so when the heating stops, so does the warmth.




Diagram showing the direct (single step) emission of radiant heat directly from source to target




  • Heat exchange occurs once (direct heating of objects)
  • Most domestic materials absorb & retain heat well
  • Less prone to infiltration loss in an enclosed space
  • Excellent priming of thermal mass = when heating stops, residual heat is left in the building.

Advantages for heaters

The advantages of radiant heating over convection:

  • Heat transferred (watts / metre / second) grows exponentially with temperature rise. Convection heat transfer grows only linearly with temperature.
  • You require less installed capacity in a radiant heating system
  • You don’t need to run it as long
  • You can apply heat only where you need it – you don’t need to heat the whole room
  • You can control it more precisely

Types of radiant heaters from Herschel

Herschel Infrared supplies

Far Infrared Panels – these are mostly used in residential and office applications.

Far Infrared Space Heaters – for heating larger enclosed spaces

Medium Infrared Space Heaters – for heating unsheltered areas (e.g. patios).

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