The heating principle
The working principle of infrared heaters is simple:
Electric infrared heaters emit electromagnetic energy as radiant heat.
The picture below displays an overview of where the infrared spectrum is located within the entire electromagnetic energy spectrum. It also shows the size of different kinds of electromagnetic waves and their typical sizes and sources in daily life.
infrared wavelength within the electromagnetic spectrum; source: www.lbl.gov (click on image to enlarge)
Array of technologies
There exists an increasingly vast array of different technologies, shapes and appearances of electric infrared heaters. The basic technical designs upon which many heaters are based, are shown in the following three pictures for some common applications:
Design example of a low-temperature far infrared heater for indoor building applications
Design example of a high temperature far infrared heater with visibly glowing heating elements for outdoors and commercial use
Design example of a high temperature far infrared ceramic heater for industrial processes
The following lists the various sub-types of electric infrared heaters which are differentiated by the wavelength range of their heat emissions, by their frontal-surface temperature and by the visibility of their heating elements.
In regards to defining wavelength regions, there is no international consensus on where one of the following 3 sub-groups begins or ends. Therefore, commonly used wavelength ranges are given:
- Short (Near) infrared ranges from (0,7-1) to 5 micrometers, equaling ca. (5.200 K to 3.000 K) to 740 K;
- Medium (Mid) infrared ranges from 5 to (25 – 40) micrometers, equaling ca. 740 K to (140 K to 92 K);
- Long (Far) infrared ranges from (25 – 40) to (200 – 350), equaling ca. (140 K to 92 K) to (19 K to 11 K);
Visibility of heating elements
Commonly, there is also made a distinction between electric infrared heaters
- with visibly glowing heating elements (in German speaking countries also called “Hellstrahler”), and
- without visibly glowing heating elements (in German “Dunkelstrahler”).
In terms of the front-face heater temperature, the proposal for the European standard EN60675 (currently in revision) may include 2 classes of electric infrared heaters:
- Low-temperature infrared heaters (with and without visibly glowing heating elements), with a minimum front-face temperature of 40°C and a maximum of 200°C / 250°C;
- High-temperature infrared heaters (with and without visibly glowing heating elements), with a minimum front-face temperature of 200°C / 250°C and higher.