Gas Radiant Heaters
by Edwin J. Cowan
Radiant heaters use the same means of heating as does the sun. A Radiant heater may make a person 5 to 10 degrees warmer similar to when that person is receiving heat rays from the sun. When a cloud blocks the sun’s rays, a person will feel instantly cooler because they are no longer receiving the sun’s direct infrared radiant heat rays. The passing cloud did not cool the surrounding air; the loss of warmth is due to the cloud blocking the transmission of heat rays from the sun, and not to a change in air temperature. Radiant heaters work in the same way.
The radiant emitter sends out heat rays in various directions. The speed of the heat rays is 186,000 miles per second. These rays do not heat the air directly. The infrared heat rays strike an object such as a person, a building, a table, or the ground and are absorbed by that object, increasing its temperature. The increased temperature of the object will heat air in contact with the object by convection, i.e., by the intimate contact of a thin layer of air to the heated object.
The geometry of our heater design plays a great part in producing a radiant heat pattern that is efficient whether close or at some distance from the heat source. Because a person located twice as far from the radiant emitter would receive only 25% of the radiant heat intensity, our design is such that the person located closer to the heat emitter receives only 25% of the more intense heat rays while the person twice as far away receives 100% of the less intense heat rays. Thus, both people are heated equally. Our heater design does not overheat the person with excess infrared heat radiation, but spreads the even infrared heat radiation over as wide a area as possible to maintain the body warmth of several people in any given area.
Various attempts have been made to compare outdoor radiant heating efficiency with that of indoor air heaters. In most cases, the basic physics of heating people are ignored. For example, national requirements are an 80% efficiency rate (of converting the heating value of gas to the energy in heated air). However, if we consider the actual heat transferred to the human body by heating air in a room, the efficiency rate is less than 1%. While the air in a room can be confined and measured for air temperature rise, outdoor air is too volumous and free moving for any attempt to measure its temperature rise. Outdoor radiant heaters work by heating people and objects directly, and not the air.
When we talk about efficiency of outdoor heating, we are talking about the ability to heat the human body!