Kees IFG (INDIRECT FIRED GAS) MAKE-UP AIR UNITS - Duct Furnace Installation & Maintenance Manual - Manual (Page 11)

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GAS CONNECTIONS (continued)
For the most satisfactory piping installation, the following
procedure should be followed. Make piping layout of the
whole installation and calculate the cubic feet of gas that
each supply pipe will carry. See piping example below.
Calculate the cubic feet of gas that each supply pipe will
carry:
Btu/Hr.
1000 Btu Natural Gas/Cu. Ft.
= Cu. Ft. Per Hour of Gas to Unit (cfh)
Unit Kilowatt
37.3 Megajoules Natural Gas/Cu Meter
= Liters per second on Gas to Unit (l/s)
NOTICE: Contact your natural gas supplier for the
Btu/Cu. Ft. content of natural gas in your area. This
may be higher or lower than the nominal 1000 Btu/Cu.
Ft. used in this example:
Refering to the piping example in figure 10, the length of
pipe from the gas meter (A) to the most remote heater (E)
is 60 feet. This distance should be used for all of the
heaters when determining the pipe size required. Based
on the column marked 60 feet in chart 3, the piping for this
example should be sized as follows:
• 450 cfh is supplied from A to B, requiring
1-1/4 inch pipe.
• 200 cfh is supplied from B to C, requiring
1 inch pipe.
• 250 cfh is supplied from B to D, requiring
1 inch pipe.
• 100 cfh is supplied from D to E, requiring
3/4 inch pipe.
• 150 cfh is supplied from D to F, requiring
1 inch pipe.
For SI calulations, refer to metric conversion chart in
general safety section of this manual.
Figure 10 - Example of Piping Layout for Determining Pipe Size
GAS METER
A
20 ft.
6.56 m.
20 ft.
6.56 m.
5 ft.
1.64 m.
5 ft.
1.64 m.
10 ft.
3.48 m.
B
C
D
F
E 10 ft.
3.28 m.
HEATER(S)
200 CFH
HEATER(S)
150 CFH
3588
HEATER(S)
100 CFH
D3588
NOTICE: If more than one gas duct furnace is to be
served by the same piping arrangement, the total
cu. ft./hr. input and length of pipe must be
considered.
NOTICE: If the gas duct furnace is to be fired with LP
gas, consult local LP gas dealer for pipe size
information. Heater installation for use with propane
(bottled) gas must be made by a qualified LP gas
dealer or installer. He will insure proper joint
compounds are used for making pipe connections;
that air is purged from lines; that a thorough test is
made for leaks before operating heater; and that it is
properly connected to propane gas supply system.
Before any connection is made to an existing line
supplying other gas appliances, contact the local gas
company to make certain that the existing line is of
adequate size to handle the combined load.
Check all connections with a soap solution before
leaving job.
HYDRONIC MODULATING GAS CONTROL
(OPTIONAL)
On units equipped with hydraulic modulating gas control,
the temperature sensing bulb for the gas valve must be
field installed in the supply ductwork. Carefully uncoil the
capillary tubing to prevent kinking or sharp bends.
Do not bend the capillary tubing within
1/2" (12.7 mm) of its connection to the bulb or the
valve. Repeated bending may cause the tubing to leak
or break.
Center and fasten the temperature sensing bulb in the
supply ductwork at least one foot downstream of the
furnace section.