The advantages of radiant heat

What is Infrared?

Human & Animal sense of comfort has evolved from Radiant heat from the sun.

Our skin has evolved to reflect and prompt us to avoid the suns hottest waves in the hundreds to thousands of degrees Centigrade – called Middle and Near (or Medium and Shortwave) infrared.

But the waves we find most comfortable are those that are absorbed by our environment and radiated back in the tens of Degrees Centigrade – called Far (or Longwave) infrared. Making our environment a thermal store during the day and continuing to release that heat long after the sun has set.

It is no surprise then, that it is Far Infrared that our skin, plus common materials in our environment absorb and emit the most efficiently.

The basis of human comfort

It is radiant heat that is biologically the most significant (60%) to our body’s sense of comfort. Convection (movement of hot or cold air) factors only 15% in our feeling of comfort, with evaporation and conduction of heat from our bodies to our clothing or other objects accounting for the remaining 25%.

Radiant heat is most keenly sensed from the top of our bodies downwards (no surprise in evolutionary terms) and is also most readily lost from the top of our bodies.

We were built primarily to absorb or emit radiant heat. With Far infrared being the biologically most significant wavelength as it is the most efficiently absorbed by the water in our skin.

The electromagnetic spectrum Infrared is a wave-band in the electromagnetic spectrum, coming just after the colour “Red”, which is how it gets its name.

It is energy, it doesn’t become “heat” until it comes into contact with an object and the energy transfers into it.

Like ripples in a pond, the waves emanate from a source (the heater) until the touch an object, at which point the energy either:

– Transmits into the object (i.e. it is “Absorbed”) – this is the property we want with our heater;

– Is bounced back from the object (i.e. it is “Reflected”);

– Continues its journey onwards (i.e. it is “Transmitted”) until the energy is eventually entirely dissipated into the environment.

This makes Infrared a very different form of Heat Transfer than warming the air, which has poor absorption qualities – mostly dependent on levels of moisture, which causes a different issue; “transmits” only poorly unless mechanically forced (e.g. by a fan) and also transfers retained heat poorly back into an environment.

Infrared is not ultraviolet and doesn’t possess any of the properties of Ultraviolet.

How does this affect how we heat ourselves?

Mean radiant temperature effect on our bodies

The radiant temperature of our environment always dominates our sense of comfort, not air temperature.  In winter our environment is “cold walls” and in summer our environment is “hot walls”.  Our bodies primarily react to this – emitting our own body heat out to the cold walls in winter, and absorbing heat energy from them in summer.

If we choose to regulate our comfort by warming or cooling air, then that air temperature must be sufficient to transfer its heat into us and it must be in motion.  If you stop either of those (i.e. turn off the heater), then you’re back to feeling the effect of the radiating environment on you. So any heater that heats air, has to be “on” to be effective and you’re only massaging a symptom of a problem.  If you have a heater on the other hand that heats the environment, then you’ve dealt with the basic problem, put energy into the environment which then radiates back for a period even when the heater is off.

Think of it this way: if air temperature defines our level of comfort, then why is an air temperature of 21 comfortable in winter, but an air temperature of 17 comfortable in summer? (And what happens if you turn off that warm or cold air…?)

This is the basis for the effectiveness of Infrared Heaters over heaters that simply warm air.

Infrared Advantages

Infrared heating has the following advantages over convection:

  • Higher rate of heat transfer per kilowatt
  • Lower kW capacity requirement;
  • Lower running time;

= higher efficiency

  • Establishes “thermal mass” – the room becomes a 360° Radiator;
  • You do not have to heat the entire volume of a room’s air to become warm;
  • You can “Zone” an infrared heater (i.e. heat just the area you want to). This is difficult to achieve with a heater that heats the air;
  • No moving parts => Lower maintenance. There are no moving parts in an Infrared Heater.
  • More accurate to control.