User Guide

Understanding Heat Spread and Throw/Distribution
4 9-200.6
Low Intensity Heat Spread/Distribution (continued)
length. The result is that tube temperatures start around 1000
to 1200°F on the burner end and fall to about 350 to 400°F on
the opposite end (the vent end).
For comfort radiant heating, once the tube temperature falls
along its length to approximately 600°F and below, the radiant
heat felt by occupants begins to decrease significantly. The
tube system still provides sensible heat to the space, which is
important for total building heating applications, but for spot
and partial area heating, these temperatures would not provide
adequate comfort levels.
The following typical tube temperature profiles will help in the
discussion toward understanding which type of tube system
configuration is appropriate with different applications.
60 Foot Straight Tube System Example
The following figure shows a typical tube system temperature
profile for a 60 foot straight tube system. The temperatures
are adequate for comfort radiant heating to just over 40 feet.
Beyond that distance, radiant heating will be negligible, as the
temperature falls below 600°F.
Figure 4.1 – 60 Ft Straight Tube Temperature
Distribution

Temperatures shown are for example purposes only. Actual results
may vary based on input rating, gas heat value, altitude, etc.
60 Foot U-Tube System Example
The following figure shows a typical 60 foot U-tube system
temperature profile (30 feet out to a 180° U-tube and 30 feet
back). The temperatures are adequate for comfort radiant
heating over the entire 30 foot length, since the temperatures
are above 600°F. Like the straight tube system, radiant
heating will be negligible over the last 20 feet of the tube
system, however since that portion is running next to the first
20 feet of the tube system where temperatures are the highest,
there is no adverse effect on radiant heating output.
Figure 4.2 – 60 Ft U-Tube Temperature Distribution

Temperatures shown are for example purposes only. Actual results
may vary based on input rating, gas heat value, altitude, etc.
Understanding these temperature distributions and resulting
effects on comfort heating will be important as application
specific examples are covered in later sections of this guide.
It is important to note that the recommended mounting heights
shown in the Performance Data are based on those units
providing comfort heating levels when mounted within the
ranges shown. From the previous discussion, it can be seen
that the heat spread and throw will increase as the mounting
height is increased. As the height specified changes, it is
important to select the unit ratings that reflect that height.
Mounting a unit higher than recommended can result in
complaints of low heat output. Mounting a unit too low can
result in complaints of too much heat. While the coverage has
changed, the infrared output has remained constant, resulting
in an increase or decrease in the intensity of the infrared
energy over the given area.
It is also important to understand that high intensity units
generally have to be mounted higher than low intensity units.
The following table summarizes this typical data.
Table 4.1
Typical Mounting Heights (ft) for Comfort Heating
Input Rating
(MBH) High Intensity Low Intensity
30
10 – 13
N/A
50 to 60
13 – 20 10 - 12
75 to 100
15 – 24 12 - 14
120 to 150
16 – 25 15 - 22
160
17 – 29
N/A
175
N/A 18 - 28
200
19 - 31 20 - 30
Infrared Heater Selection Procedure
The proper selection of heaters in the design and layout of an
infrared heating system is determined by a number of factors,
but primarily by the following:
Clearance to Combustibles
Clearance to combustibles is also a critical in selection of the
unit. Please refer the unit Installation and Service Manual for
complete details. Care must be taken to ensure that the units
have adequate clearance around them so that combustible
materials will not ignite or be damaged. As a guideline,
certified minimum distance to combustible material is based on
the combustible material surface not exceeding 90˚F above
ambient (160˚F typical). This does not apply to just wood,
drywall, etc., but some other commonly encountered items as
well. Below are some examples,
 Vehicles parked below the heater.
 Sprinkler heads near the unit.
 Storage of combustible materials. This is sometimes
overlooked and requires additional action on the part of
the building owner/operator. In these locations, signs
shall be clearly posted in the vicinity of the heater where
readily apparent to material handlers to indicate the
maximum permissible stacking height to maintain
required clearances from the heater. See Figure 5.2 on
the following page for additional details.
Approximate Tube Temp Across Tube System
60 Foot Straight Tube
200
400
600
800
1000
0 102030405060
Feet from Burner
°F
Approximate Tube Temp Across Tube System
60 Foot U-Tube
600
700
800
900
1000
0 5 10 15 20 25 30 35
Feet from Burner
°F