Reznor X Unit Installation Manual - Manual (Page 13)

Form I-X, P/N 150491 R10, Page 13
6.3.3 Constructing
Bypass Duct
Top View
of Furnace
Control Side
Bypass Duct A
2” (51mm) minimum
18” (457mm) 18” (457mm)
FIGURE 12 - Bypass Duct Bypass CFM
"A" Width Pressure Drop through the Furnace
inches mm 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50
3" 76 490 530 610 700 780 830 900 960 1010
4" 102 630 750 870 980 1090 1160 1250 1310 1400
5" 127 850 1010 1190 1300 1410 1520 1640 1730 1810
6" 152 1050 1290 1480 1650 1800 1940 2090 2200 2320
7" 178 1250 1510 1760 1960 2180 2320 2500 2650 2800
8" 203 1490 1810 2100 2350 2560 2760 2940 3110 3290
9" 229 1700 2100 2400 2700 2970 3200 3400 3600 3800
10" 254 1920 2350 2760 3090 3650 4020 4300 4550 4800
When the CFM of air throughput is greater than desirable or permissible for the unit,
a bypass duct may be constructed. Follow these instructions to determine the correct
size of the bypass duct.
of air at the end of the duct. Or, baffles may be inserted between the blower and the
heater to assure an even flow of air across the heat exchanger.
WARNING
The furnace MUST be installed on the positive pressure side of the air-
circulating blower. See Hazard Levels, Page 2 .
Directions for Sizing Bypass Duct
1) From the tables in Paragraph 6.3.1, find the pressure
drop (P.D.) and the allowable CFM for the duct
furnace that is being installed.
EX: Size X150 @ 50°F Temperature Rise; P.D. 38;
CFM 2210
2) Subtract the allowable CFM from the actual CFM of
the installation to determine how much air must be
diverted through the bypass duct.
EX: Actual Blower CFM is 3000; 3000 minus
allowable CFM of 2210 = 790
3) Go to the column in the bypass CFM chart that is
closest to the pressure drop through the heater. Move
down in that column until you find the CFM closest to
the answer in Step 2).
EX: Go to P.D. column .40; move down to 900
4) Move to the left column to find out the required size
of the bypass duct.
EX: Bypass Duct should be 3" (76mm).
Locate the bypass duct on the side of the furnace oppo-
site the controls and 2" from the heat exchanger side
panel. Extend the bypass duct 18" (457mm) beyond the
furnace on both the inlet and outlet ends.
NOTE: Not all capacities are covered in this chart. If
your installation is not covered, consult your Reznor
representative or the factory to determine the appropriate
size of the bypass duct.
6.3.4 Duct
Connections
Size
75,
100
125
150,
175
200,
225
250,
300
350 400
G
12-1/2 15-1/4 20-3/4 26-1/4 34-1/2 40 45-1/2
(318) (387) (527) (667) (876) 1016 (1156) G
3/4 (19)
3/4
(19)
18 (457)
FIGURE 13 - Duct
Connection Dimensions
- inches (mm)
IMPORTANT NOTE: A minimum horizontal duct length of 18 inches (457mm) is required at the furnace discharge
before any vertical rise is made in front of the drafthood relief opening. This is required to prevent interference with the
built-in drafthood.
Requirements and
Suggestions for
Connecting and
Installing Ducts
• Type of Ductwork - The type of duct installation to be used depends in part on the
type of construction of the roof (whether wood joist, steelbar joist, steel truss, pre-
cast concrete) and the ceiling (whether hung, flush, etc.).
• Ductwork Material - Rectangular duct should be constructed of not lighter than
No. 26 U.S. gauge galvanized iron or No. 24 B & S gauge aluminum.
• Ductwork Structure - All duct sections 24 inches or wider, and over 48 inches
in length, should be cross broken on top and bottom and should have standing
seams or angle-iron braces. Joints should be S and drive strip, or locked.