User Guide

Infrared Heater Selection Procedure – Total Building Heating
8 9-200.6
Total Building Heating
Total building heating applications involve replacing the
building heat loss with at least the same amount of heat,
placed near the areas of greatest heat loss. Total building
heating applications with infrared are best accomplished using
low intensity tube heaters. However, Modine offers a number
of different heating equipment options for building heating, so
all options should be considered. This guide will only focus on
an infrared heater layout.
The selection process for infrared in a total building heating
application is more of an art than a science. One must not only
know the heat loss of the building and the dimensions, but
other characteristics such as the available mounting height,
clearance to combustibles, and building layout which includes
the shape of the area, location of utilities, physical interference
from equipment such as lights or overhead cranes, etc. The
selection/layout process is outlined below.
Determine Available Ratings
After the type of infrared heater to be used has been
determined, high-intensity, low-intensity, or a combination of
both, available ratings are determined based on the mounting
height and required clearances to combustibles as indicated in
the Performance Data tables on page 12.
Example 1: A building has a ceiling height of 18 feet. Low
intensity units are to be used. What are the available unit sizes
that should be considered in the layout?
From the Performance Data, the applicable unit ratings are
125,000 Btu/hr for mounting between 15 to 22 feet, 150,000
Btu/hr for mounting between 15 to 25 feet, and 175,000
Btu/hr for mounting between 18 to 28 feet. Each requires a
minimum of 12" clearance to combustibles from the top.
Based on the required clearance, the mounting height
should not exceed 17 feet (i.e. ceiling height of 18 feet –
12” = 17 feet). This would make the 175,000 Btu/hr unit a
less likely choice since it is recommended to be mounted
above that height.
Figure 8.1 - Mounting Height for Example 1
Determine the Number of Heaters Required
With available ratings known, the total number of heaters
required can be determined by dividing the total building heat
loss by the input rating of each heater. Multiple ratings may be
used based on the building layout and dimensions. Refer to
the following section titled “Heater Placement” for information
on selection based on layout.
Heater Placement
Placement of the heaters should be concentrated where heat
loss is greatest. In the case of total building heating, the heat
loss occurs mainly along the perimeter of the building.
While it makes sense to place the heaters along the perimeter,
if the distance between parallel walls exceeds 100', it is best to
use a combination approach of perimeter and row heating.
The heater capacity along the perimeter should be at least
80% of the total system capacity with the remaining maximum
20% of the total system capacity located in parallel rows
toward the center of the building. The center rows are used to
compensate for the roof heat losses.
Example 2: Expanding on Example 1, the building is 200' long
x 160' wide with a calculated heat loss of 1,600,000 Btu/hr.
Example 1 determined that units rated 125,000 or 150,000
Btu/hr should be considered. Which will work best?
If the building heat loss is 1,600,000 Btu/hr, the number of
125,000 Btu/hr units required would be 13 (1,600,000 /
125,000 = 12.8  13 units). For 150,000 Btu/hr rated units,
the quantity required would be 11 units. Reviewing the
figure for Example 2 on the following page, there will be 3
units required to cover each of the 200’ long walls (using 60
foot straight tube systems). Since the distance between
parallel walls exceeds 100', it is best to use a combination
of perimeter and row heating. Adding a third row in the
center will require another 3 units. So far, this is 9 units
total, and the 160’ long ends of the building need to be
covered. Given the distance, the minimum tube length
should be 60’ with 2 systems required on each end. The
choices at this point are:
 Use (13) 150,000 Btu/hr units with 60’ straight tube
systems. Total input will be 1,950,000 Btu/hr.
 Use (13) 125,000 Btu/hr units with 60’ straight tube
systems. Total input will be 1,625,000 Btu/hr.
 Use (13) units that are a combination of 125,000 and
150,000 Btu/hr units. Total input will be based on the
mix of the ratings selected.
All three choices are acceptable. The use of (13) 125,000
Btu/hr units may have trouble maintaining design
temperature on the coldest days that fall below the winter
design temperature. The 150,000 Btu/hr units will
normally accommodate even the coldest days, but may be
oversized for normal conditions (operating on zone
thermostats may minimize cycling).
Note that the layout solutions above meet the recommended
80%/20% rule for capacity location in a combination perimeter
and row layout. With 10 of the 13 units located along the
perimeter, assuming all units are of the same rating, 77% of
the layout capacity is on the perimeter with 23% of the capacity
in the center row.
It is also important to note that these three solutions are by no
means the “correct answers”, as there could be considerably
more “correct answers”. There are some other factors that
should considered that may affect the design of the layout
selected. These are examined in the section titled “Additional
Considerations (All Applications)” on page 9.