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Radiant Heating

RADIANT principles apply to equip ment with radiant source temperatures ranging from 300 to 5000°F. Radiant equipment with source temperatures in this range is categorized into three groups as follows:

• Low intensity
• Medium intensity
• High intensity
Radiant equipment with source temperatures from below room temperature to 300°F is classified as panel heating and cooling equipment.

Low-intensity source temperatures range from 300 to 1200°F. A typical low-intensity heater is mounted on the ceiling and may be constructed of a 4 in. steel tube 20 to 30 ft long. A gas burner inserted into the end of the tube raises the tube temperature, and because most units are equipped with a reflector, the radiant energy emitted is directed down to the conditioned space.

Medium-intensity source temperatures range from 1200 to 1800°F. Typical sources include porous matrix gas-fired infrared units or metal sheathed electric units.

High-intensity radiant source temperatures range from 1800 to 5000°F. A typical high-intensity unit is an electrical reflector lamp with a resistor temperature of 4050°F.

Low-, medium-, and high-intensity infrared heaters are frequently applied in aircraft hangars, factories, warehouses, foundries, greenhouses, and gymnasiums. They are applied to open areas including loading docks, racetrack stands, under marquees, outdoor restaurants, and around swimming pools. Infrared heaters are also used for snow and ice melting

When infrared is used, the environment is characterized by

1. A directional radiant field created by the infrared heaters
2. A radiant field consisting of reradiation and reflection from the walls and/or enclosing surfaces
3. Ambient air temperatures often lower than those found with convective systems The combined action of these factors determines occupant comfort
and the thermal acceptability of the environment.


Infrared heating units are effective for spot heating. However, due to efficient performance, they are also used for total heating of large areas and entire buildings. Radiant heaters transfer energy directly to solid objects. Little energy is lost during transmission because air is a poor absorber of radiant heat.

As infrared energy warms floors and objects, they in turn release heat to the air by convection. Reradiation to surrounding objects also contributes to comfort in the area. An energy-saving advantage is that radiant heat can be turned off when it is not needed; when it is turned on again, it is effective in minutes.

Human comfort is determined by the average of mean radiant and dry-bulb temperatures. With radiant heating, the dry-bulb temperature may be kept lower for a given comfort level than with other forms of heating. As a result, the heat lost to ventilating air and via conduction through the shell of the structure is proportionally smaller, as is energy consumption. Infiltration loss, which is a function of temperature, is also reduced.

Due to the unique split of radiant and convective components in radiant heating and cooling, air movement and stratification in the conditioned space is minimal. This reduces the infiltration and transmission heat losses.


Gas Infrared

Modern gas-fired infrared heaters burn gas to heat a specific radiating surface. The surface is heated by direct flame contact or with combustion gases.
.The wavelength span over which radiation from a heated surface is distributed can be controlled by design. The specific radiating surface of a properly designed unit directs radiation toward the load. Heaters are available in the following types

Indirect infrared radiation units are internally fired and have the radiating surface between the hot gases and the load. Combustion takes place within the radiating elements, which operate with surface temperatures up to 1200°F. The elements may be tubes or panels with metal or ceramic components. Indirect infrared radiation units are usually vented and may require eductors.

Radiant Floor Heating



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