User Guide

Understanding Heat Spread and Throw/Distribution
9-200.6 3
Before selection occurs, a solid understanding of the infrared
heater heat spread/distribution is required to avoid potential
misapplications of the equipment. This section provides the
basic information to gain this understanding.
High Intensity Heat Spread/Throw
Heat spread (width), as shown in Figure 3.1 is dependant on
the mounting height and relatively unaffected by the mounting
angle. The spread at floor level is approximately twice the
mounting height. However, someone occupying the edge of
that space will feel minimal heat. To cover an entire area up to
5 feet high (shoulder level for the average worker), the
mounting height should be approximately 5 feet above half the
distance of the desired width. For example, if the shoulder
height area width is to be 40 feet wide, the mounting height
should be approximately 25 feet above the floor (5 feet + ½ x
40 feet = 25 feet). The actual floor level spread will be
approximately 50 feet, but the radiated infrared heat is
negligible at the edge of that area.
Figure 3.1 – High Intensity Heat Spread Width
Heat distribution (throw) is dependent on both the mounting
height and the mounting angle. At a 10° mounting angle, the
heat throw at a height of 5 feet will be approximately ½ x (the
mounting height – 5 feet) in one direction and 1 ½ x (the
mounting height – 5 feet in the other direction). For example, if
the unit is mounted at 25 feet above the floor, then the spread
will be 25 feet – 5 feet = 20 feet x ½ = 10 feet in one direction
and 25 feet – 5 feet = 20 feet x 1 ½ = 30 feet in the other
direction. The total throw would be 10 feet + 30 feet = 40 feet.
Selection of mounting angle is influenced by the application,
which will be discussed in a later section.
Figure 3.2 – High Intensity Heat Distribution/Throw
Low Intensity Heat Spread/Distribution
Heat spread (width), as shown in Figure 3.3 is dependant on
both the mounting height and mounting angle. The spread at
floor level for a unit mounted at 0° is roughly twice the
mounting height. However, someone occupying the edge of
that space will feel very little heat. To cover an entire area up
to 5 feet high (shoulder level for the average worker), the
mounting height should be approximately 5 feet above half the
distance of the desired width. For example, if the shoulder
height area width is to be 30 feet wide, the mounting height
should be approximately 20 feet above the floor (5 feet + ½ x
30 feet = 20 feet). Note that the actual floor level spread will
be approximately 40 feet, but the infrared heat is negligible at
the edge of that area.
Figure 3.3 – Low Intensity Heat Spread Width
Heat distribution is dependent on the type of tube system used
(straight versus U-tube) and the length. Heat intensity along
the length of the tube system varies considerably. A solid
understanding of this distribution is key to ensuring that the
equipment is properly specified for the application.
Misunderstanding is the number one cause of complaints of
insufficient heat.
The first step toward understanding the distribution of radiant
heat is gaining an appreciation for the significant effect that
temperature has on radiant intensity. The basic equation for
calculating radiant intensity is:
R (Watts/in
2
) =  x σ x (Temp)
4
, where:
 = Emissivity of the emitter (tube system)
σ = Stefan-Boltzmann Constant
Temp = Temperature difference between the emitter
(tube system) and the absorber (people)
Without going into the theory behind the calculations, the
important item to note is that the radiant intensity varies by the
absolute temperature difference raised to the 4
th
power
(multiplied by itself 4 times), which tells us that temperature
has a significant effect on radiant intensity. Since the tube
system is a long heat exchanger, it is losing heat along its
Height
Spread Width = (Height – 5ft) x 2
Spread
Width
5’
H
1.5H @ 10°
3.5H @ 35°
0.5H @ 10°
0.0H @ 35°
5’
Height
Total Spread = (Height
–
5ft) x 2 [ 0° mounting angle]
Total Spread = (Height – 5ft) x 4 [45° mounting angle]
Total
Spread