How infrared heaters work

The natural oscillation of molecules in heat conductors generates infrared heat radiation, which corresponds to the radiation spectrum of the sun.

Infrared rays penetrate air by 98%. The energy contained in them is much more effectively absorbed by the space envelope and objects (furnishings, residents). The air is heated secondarily, by the reflective heat dissipation of the surrounding surfaces and objects in the room.

By contrast, convection heaters (radiators), primarily heat rooms by heating the room air, the worst heat carrier. The heated air rises, cold air flows from below, and a convection current is created.

The substantial temperature differences between heated indoor air and cold outer wall surfaces are also accompanied by uneven distribution of moisture.

Unlike conventional heaters, infrared heaters ensure a warm space envelope, lower air temperature, and a more even distribution of moisture. The air is fresher overall, and your feet stay comfortably warm.

The thermal energy obtained from the conversion of the supplied electrical energy is comprised of the radiation component, the convection component and the heat conductivity component.

The radiation efficiency is the radiation component of the total thermal output.

Economic efficiency

Heating with electricity is only expensive if you try to heat air in the first place. Infrared heaters, however, heat basically the space envelope. This is why 3-4° C less air temperature is needed. Since every 1° C higher indoor air temperature requires 6% to 7% more heating energy, more than 20% heating energy can be saved in total.

  • Reduced ventilation losses:
    Less heating energy is lost through ventilation because of the lower indoor air temperature.
  • Avoidance of transmission heat losses (dry / damp walls):
    The moistening of exterior walls leads to reduced insulation and thus to low temperatures on the insides of the outer walls (even 4% humidity reduces the insulation value by about 50%).
    Infrared-heated wall surfaces, however, are kept warm and have higher temperature than the air. The high surface temperature precludes the absorption of water vapour through the walls and prevents transmission losses.
    Radiant heat
  • Low investment costs
  • No additional costs (e.g. no chimney sweep)
  • No maintenance
  • 100% renewably operable
  • No boiler room or fireplace needed
  • No heating pipes necessary
  • No risk of water damage due to heating pipe breakage


Thermal comfort

In terms of heating and air conditioning, (thermal) comfort refers to ambient temperatures and air conditions which make people feel most comfortable. A heating system should contribute to comfortable indoor climate.

The objective benchmark for comfort is the temperature felt. It depends on

  • the room air temperature
  • the radiation temperature of the environment
  • the air temperature distribution (air stratification)
  • the airflow (draft)
  • the relative air humidity


Radiant heat

comfort curve

If the room walls have strongly disparate surface temperatures, this can affect the comfort due to the so-called radiant temperature asymmetry.

Even temperature differences of 1 ° C per height metre are perceived as disturbing. This vertical distribution is also referred to as air temperature stratification. The temperature profile should be as constant as possible.

The warmer the air, the more moisture it can absorb. The relative humidity is the ratio of the current amount of water in the air to the maximum possible amount of water at a given air temperature. An air humidity of 40-50% is perceived as particularly comfortable.

During ventilation, cold outside air with only low absolute humidity is warmed up to room temperature, and the relative humidity in the room continues to drop.

At a relative humidity of 30-70%, air movement of up to 20 cm/s and far-reaching temperature uniformity of the room surfaces, the (thermal) comfort depends on the operative temperature only (= average of room air temperature and medium radiation temperature of the space envelope).


Radiant heat


We tend to feel better when the radiation temperature is higher than the air temperature. Since infrared heaters generate radiation temperatures that are higher than air temperatures, they are also preferable to convection heaters for comfort reasons.


Physical characteristics of radiant heaters

Radiant heat

The physical fundamentals of convection heaters and radiant heaters are completely different:

In the convection heating (air heating), heat is transferred by the flow of warm air. According to the first and second law of thermodynamics, this requires temperature differences.

In the case of radiant heating, according to Max Planck’s quantum mechanics, the heat transfer takes place without any conveying medium by thermal radiation alone. It is based on the following physical principles:

  • The heat radiation of an infrared radiant heater is an electromagnetic wave similar to the light, the electricity, the microwave, and the radio waves, all of which move at the speed of light.
  • The wavelengths considered as infrared rays for heating purposes with temperatures of up to 80°C are in the narrow band between 3 and 50 µm (microns). Like all temperate and warm surfaces, they are harmless to health. There is no electrosmog as well.
  • Each surface is able to absorb heat rays (energy gain through absorption) and send them out (energy loss through emission). Radiant energy is thus simultaneously absorbed and emitted by a temperature-controlled surface.
  • Heat radiation does not heat air, but only solid and liquid matter. The room air is permeable to heat rays and thus remains cool and pleasant. The temperatures of the room enclosure surfaces are higher than the air temperature. Therefore, the heating of adjacent air layers is convective only indirectly, through the warmer surfaces. Also, energy is saved by ventilation due to the low air temperatures.
  • Due to the almost dormant air (only very little dust dispersion), ventilation is required less often. This, in turn, saves energy.
  • Infrared heat radiation (> 3μm) does not penetrate normal glass. The heat radiation remains in the room./li>

The task of a radiant heater is solely to create tempered surfaces, which then ensure a pleasant indoor climate by (infrared) heat rays. The ceiling and the walls are particularly suitable for placing the radiant surfaces on them.


Radiant power

The radiant power of a tempered surface is described by the Stefan Boltzmann law. Thus, it is proportional to the fourth power of the absolute temperature of a surface. This means that heat rays are emitted regardless of the ambient temperature, solely due to the surface temperature.

Radiant heat

In contrast, a convection heater requires “excess temperatures” to function. The heat output is thus proportional to the temperature difference between the radiator and the room air.


Radiation exchange

All surfaces in rooms absorb and emit heat rays. The higher tempered surface gives off energy by radiation to the lower tempered one and vice versa. The radiation exchange is thus proportional to the difference between the two radiant powers.

Radiant heat

Due to the radiation exchange, the surface temperatures in the room become aligned. Absorbed and emitted heat energies are then equal. Evenly tempered surfaces appear, including the furniture – you feel complacent and comfortable.


The difference between radiant power and radiation exchange

Example 1:

T1=80°C (the radiant panel) and

T2=20°C (wall)

The difference (radiation exchange) is very large.


Beispiel 2:

T1=80°C (the radiant panel) and

T2=50°C (a moderately tempered radiant panel)

The difference (radiation exchange) is substantially smaller.

The radiant power is overall higher.


Example 3:

T1=80°C (the radiant panel) and

T2=80°C (another radiant panel opposite to it)

The difference (radiation exchange) is equal to zero.

However, the radiant power for the room is doubled.


It is self-evident that radiation exchange does not correspond to radiation power.

Consequently, the formula for the radiation exchange can in no case be used to determine the radiant power.

Health aspects

Air turbulence

House dust allergy and asthma sufferers are sensitized or allergic to the dust mite droppings, which can trigger rhinitis, itching, and asthma. These droppings adhere to house dust and are “stirred up” with every form of convection. The lower the convection rate of a heater, the better for an allergic person.

Radiant heat

Dry heating air

Conventional (convection) heaters create the feeling of dry heating air. Low relative humidity can cause health problems:

  • Decreased breathing performance: the oxygen gets worse into the bloodstream through the lungs.
  • Skin moisture is closely linked to humidity. Therefore, our skin needs sufficient humidity, so as not to dry out. Also, our susceptibility to skin irritations and redness or even inflammation is increased by low humidity.
  • The evaporation protection of mucous membranes is quite low. Therefore, they are prone to dry-out and need high humidity to maintain their functions. Low moisture in the nasal mucous membrane can cause an increased incidence of nosebleeds. Also, the immune defence of the mucous membranes can get weaker (increased risk of colds) and their ability to metabolize can decrease.
  • Dry eyes: Many people, especially contact lens wearers, suffer from red, burning or itchy eyes at low relative humidity. The wearing comfort of contact lenses is limited. This is why ophthalmologists generally recommend avoiding dry heating air and drafts.

Blood circulation

In physiotherapy, infrared C radiation is used in cases of musculoskeletal overload and in the treatment of circulatory disorders, as infrared heating tends to have a positive medical and therapeutic effect.


Radiant heat

Risk of mold growth

The moisture contained in the warm room air condenses by cooling on the cold inner surfaces of the outer walls. Condensate can cause mold formation, especially in room corners, behind furniture, curtains, and in other concealed areas that cool more than the rest of the wall. For mold growth to be avoided, humidity should never rise above 80% – even at individual points.

Possible symptoms caused by mold are multifarious and quite unspecific. They include:

  • Cough
  • Rhinitis
  • Conjunctivitis
  • Asthma
  • Skin rashes
  • Migraine
  • Gastrointestinal complaints
  • Joint pain

Since infrared heaters keep the walls warmer than the air, condensation does not even happen. The already contained moisture is removed from the walls.