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105564-UIM-A-0205

4

Unitary Products Group

DUCTWORK INSTALLATION AND SUPPLY PLENUM 

CONNECTION

A proper Heat Loss/Gain Calculation should be done on all
installations for proper application of equipment. From this
the ductwork sizing can be calculated, ACCA Manual J and
D and industry standards are helpful.

Attach the supply plenum to the furnace or coil outlet duct
connection flanges. This is typically through the use of S
cleat material when a metal plenum is used. The use of an

approved flexible duct connector is recommended on all installations to
prevent noise transmission. All connections should be sealed to prevent
air leakage. Sheet metal should be crosshatched to eliminate any pop-
ping when the indoor fan is energized.

When replacing an existing furnace, if the existing supply plenum is not
the same size as the new furnace then the existing plenum must be
removed and a new plenum installed that is of the proper size for the
new furnace. The minimum plenum height is 12” (30 cm). If the plenum
is shorter than 12” (30 cm) the turbulent air flow may cause the limit
controls not to operate as designed if at all.

The duct system is a very important part of the installation. 

If the duct

system is improperly sized the furnace will not operate properly.

The ducts attached to the furnace plenum should be of sufficient size so
that the furnace operates at the specified external static pressure and
within the air temperature rise specified on the nameplate.

Table 2 is a guide for determining whether the rectangular duct system
that the furnace is being connected to be of sufficient size for proper fur-
nace operation.

Use the Example below to help you in calculating the duct area to deter-
mine whether the ducts have sufficient area so that the furnace oper-
ates at the specified external static pressure and within the air
temperature rise specified on the nameplate.

The following are general duct sizing guidelines that may not serve to
requirements of every application.

Example: The furnace input is 80,000 BTUH, 1,200 CFM blower
requirement. The recommended duct area is 216 sq.in, there are two 8
x 12 rectangular ducts attached to the plenum and there are two 7 inch
round ducts attached to the furnace.

1.

Take 8 x 12, which equals 96 square inch x 2 = 192 square inches
then go to round duct size located in Table 3.

2.

The square inch area for 7 inch round ducts, 38.4 square inch x 2
= 76.8 square inches,

3.

Then take the 192 square inch from the rectangular duct and add it
to the 76.8 square inch of round duct. The total square inch of duct
attached to the furnace supply plenum is 268.8 square inches.
This exceeds the recommended 216 square inch of duct.

In this example, the duct system attached to the plenum has a sufficient
area so that the furnace operates at the specified external static pres-
sure and within the air temperature rise specified on the nameplate.
Providing the return duct is properly sized as well.

1.

The Air Temperature Rise is determined by subtracting the Return
Air Temperature Reading from the Supply Air Temperature Read-
ing.

2.

The External Static Pressure is determined by adding the Supply
Duct Static Pressure reading to the Return Duct Static Pressure
reading and adding the pressure drop across any applied coil.

TABLES 2 AND 3 are to be used as a guide only to help the installer
determine if the duct sizes are large enough to obtain the proper air flow
(CFM) through the furnace. TABLES 2 and 3 ARE NOT to be used to
design ductwork for the building where the furnace is being installed.
There are several variables associated with proper duct sizing that are
not included in the tables. To properly design the ductwork for the build-
ing, Refer to the ASHRAE Fundamentals Handbook, Chapter on
“DUCT DESIGN” or a company that specializes in Residential and Mod-
ular Home duct designs.

IMPORTANT: 

The minimum plenum height is 12” (30 cm). The furnace

will not operate properly on a shorter plenum height. The minimum rec-
ommended rectangular duct height is 4” (10 cm) attached to the ple-
num.

IMPORTANT: 

The air temperature rise should be taken only after the

furnace has been operating for at least 15 minutes. Temperatures and
external static pressures should be taken 6” (15 cm) past the first bend
from the furnace in the supply duct and the return duct. If an external fil-
ter box or an electronic air cleaner is installed, take the return air read-
ings before the filter box or air cleaner.

The duct system must be properly sized to obtain the correct airflow
for the furnace size that is being installed.
Refer to Table 7 and the furnace rating plate for the correct rise
range and static pressures
If the ducts are undersized, the result will be high duct static pres-
sures and/or high temperature rises which can result in a heat
exchanger OVERHEATING CONDITION. This condition can result
in premature heat exchanger failure, which can result in personal
injury, property damage, or death.

TABLE 2: 

Minimum Duct Sizing For Proper Airflow

Input/Cabinet

Nominal Airflow

Return

1

Rectangular

2

Round

2

Supply

3

Rectangular

2

Round

2

MBTU/H (kW)

CFM (m³)

In² (cm²)

in. x in. (cm x cm)

in. (cm) dia.

In² (cm²)

in. x in. (cm x cm)

in. (cm) dia.

40/A (11.7)

1,200 (33.98)

280 (711)

14 x 20 (35.6 x 50.8)

18 (45.7)

216 (549)

12 x 18 (30.5 x 45.7)

16 (40.6)

60/B (17.6)

1,200 (33.98)

280 (711)

14 x 20 (35.6 x 50.8)

18 (45.7)

216 (549)

12 x 18 (30.5 x 45.7)

16 (40.6)

80/B (23.4)

1,200 (33.98)

280 (711)

14 x 20 (35.6 x 50.8)

18 (45.7)

216 (549)

12 x 18 (30.5 x 45.7)

16 (40.6)

80/C (23.4)

1,600 (45.31)

360 (914)

18 x 20 (45.7 x 50.8)

22 (55.8)

280 (711)

14 x 20 (35.6 x 50.8)

18 (45.7)

80/C (23.4)

2,000 (56.63)

440 (1,118)

20 x 22 (50.8 x 55.8)

24 (60.9)

390 (991)

16 x 22 (40.6 x 55.8)

22 (55.8)

100/C (29.3)

1,600 (45.31)

360 (914)

18 x 20 (45.7 x 50.8)

22 (55.8)

280 (711)

14 x 20 (35.6 x 50.8)

18 (45.7)

100/C (29.3)

2,000 (56.63)

440 (1,118)

20 x 22 (50.8 x 55.8)

24 (60.9)

390 (991)

16 x 22 (40.6 x 55.8)

22 (55.8)

120/D (35.2)

2,000 (56.63)

440 (1,118)

20 x 22 (50.8 x 55.8)

24 (60.9)

390 (991)

16 x 22 (40.6 x 55.8)

22 (55.8)

135/D (39.6)

2,000 (56.63)

440 (1,118)

20 x 22 (50.8 x 55.8)

24 (60.9)

390 (991)

16 x 22 (40.6 x 55.8)

22 (55.8)

NOTE: This chart does not replace proper duct sizing calculations or take into account static pressure drop for run length and fittings. Watch out for the temperature rise and static pres-
sures.

1.

Maximum return air velocity in rigid duct @ 700 feet per minute (19.82 m

3

 / minute).

2.

Example return main trunk duct minimum dimensions.

3.

Maximum supply air velocity in rigid duct @ 900 feet per minute (25.49 m

3

 / minute).

TABLE 3: 

Round Duct Size

Round Duct Size

Calculated Area For Each Round Duct Size

inches (cm)

Sq.in (cm

2

)

5 (13)

19.6 (126)

6 (15)

28.2 (182)

7 (18)

38.4 (248)

8 (20)

50.2 (324)

9 (23)

63.6 (410)

10 (25)

78.5 (506)

11 (28)

95 (613)

12 (30)

113.1 (730)

13 (33)

132.7 (856)

14 (36)

153.9 (993)

Summary of Contents for FC9S

Page 1: ...8 TWINNING AND STAGING 9 COMBUSTION AIR AND VENT SYSTEM 11 CONDENSATE PIPING 18 SAFETY CONTROLS 18 START UP AND ADJUSTMENTS 19 WIRING DIAGRAM 25 LIST OF FIGURES Dimensions 5 Furnace Base Rectangular Blockoff Panel 6 Gas Valve 6 Gas Piping 6 Electrical Wiring 8 Line Wiring Connections 9 Single Stage Heat Thermostat Connections 9 Single Stage Heating and Two Stage Cooling Thermostat Connections 9 Ac...

Page 2: ...e ational vehicles Failure to carefully read and follow all instructions in this manual can result in furnace malfunction death personal injury and or property damage Furnaces for installation on combustible flooring shall not be installed directly on carpeting tile or other combustible material other than wood flooring Check the rating plate and power supply to be sure that the elec trical charac...

Page 3: ... required for passage to the front when servicing or for inspection or replacement of flue vent connections In all cases accessibility clearances shall take precedence over clear ances for combustible materials where accessibility clearances are greater Installation in a residential garage 1 A gas fired furnace for installation in a residential garage must be installed so the burner s and the igni...

Page 4: ...ssure drop across any applied coil TABLES 2 AND 3 are to be used as a guide only to help the installer determine if the duct sizes are large enough to obtain the proper air flow CFM through the furnace TABLES 2 and 3 ARE NOT to be used to design ductwork for the building where the furnace is being installed There are several variables associated with proper duct sizing that are not included in the...

Page 5: ... 1 for unit and plenum dimensions Attic installations must meet all minimum clearances to combustibles and have floor support with required service accessibility The supply air temperature MUST NEVER exceed the Maximum Supply Air Temperature specified on the nameplate Operating the furnace above the maximum supply air temperature will cause the heat exchanger to overheat causing premature heat exc...

Page 6: ...uctions in this section specify the type of gas approved for this furnace only use those approved gases The instal lation of a drip leg and ground union is required Refer to Figure 4 IMPORTANT An accessible manual shutoff valve must be installed upstream of the furnace gas controls and within 6 feet 1 8 m of the fur nace The furnace must be isolated from the gas supply piping system by closing its...

Page 7: ...cing a wrench to the body of the gas valve will damage the valve causing improper operation and or the valve to leak TABLE 5 High Altitude Conversion 40 120 MBTUH Models Type Of Gas Orifice at Sea Level 2 000 ft 610 m 3 000 ft 914 m 4 000 ft 1219 m Natural 45 46 47 47 Propane 55 55 55 55 Type Of Gas 5 000 ft 1524 m 6 000 ft 1829 m 7 000 ft 2134 m 8 000 ft 2438 m Natural 47 48 48 49 Propane 56 56 5...

Page 8: ...ternate wiring method is to use a field provided 2 5 08 cm x 4 10 2 cm box and cover on the outside of the furnace Route the furnace leads into the box using a protective bushing where the wires pass through the furnace panel After making the wiring connections replace the wiring box cover and screws 3 The furnace s control system requires correct polarity of the power supply and a proper ground c...

Page 9: ... using the same duct system it is very important that the two furnace cir culating air blowers operate in unison If one blower starts before the second blower the duct system will become pressurized and the blower on the second furnace will turn backwards causing the second furnace to overheat resulting in damage to the furnace Twinning is used to make two furnaces operate in tandem using one duct...

Page 10: ... then will shut off at the same time Continuous Fan On a thermostat call for continuous fan G signal both furnace blowers will come on at the same time in cooling speed and will stay on until the G signal is removed STAGING In applications where more heating capacity or more airflow capacity is needed than what one furnace can deliver twinning can be used to make two furnaces operate in tandem usi...

Page 11: ...low a maximum of 5 elbows in the combustion air piping and a maximum of 5 elbows in the vent piping 4 Three vent terminal elbows two for vent pipe and one for air intake pipe are already accounted for as vent termination 5 Combustion air and vent piping must be of the same diameter 6 All combustion air vent pipe and fittings must conform to American National Standards Institute ANSI standards and ...

Page 12: ...on air systems from the furnace to the out side termination B Ventilated combustion air systems from the furnace to the attic or crawl space termination 6 Disassemble the combustion air and vent piping apply cement primer and the cement per the manufactures instructions Primer and cement must conform to ASTM D2564 for PVC or ASTM D2235 for ABS piping 7 All joints must provide a permanent airtight ...

Page 13: ...30 kW 36 inches 91 cm for models 100 000 BTUH 30 kW Two pipe direct vent applications 9 inches 23 cm for models 50 000 BTUH 15 kW 12 inches 30 cm for models 50 000 BTUH 15 kW Single pipe applications 4 feet C Clearance to permanently closed window 4 Feet 4 Feet D Vertical clearance to ventilated soffit located above the terminal within a horizontal distance of 2 feet 61 cm from the center line of ...

Page 14: ...combustion air systems must be installed so the vent and the combustion air pipes terminate in the same atmospheric zone Refer to Figures 15 or 16 VENTING MULTIPLE UNITS Multiple units can be installed in a space or structure as either a single pipe configuration or a two pipe configuration The combustion air side of the single pipe configuration shown in Figure 20 is referred to in these instruct...

Page 15: ...ill bring air in from the outdoors to the furnace combustion air intake collar on the burner box The second pipe Shown in Figure 19 is the furnace vent pipe The combustion air intake pipe should be located either through the wall horizontal or side vent or through the roof vertical vent Care should be taken to locate side vented systems where trees or shrubs will not block or restrict supply air f...

Page 16: ...he louver is in the fully open position This type of installation requires that the supply air to the appli ance s be of a sufficient amount to support all of the appliance s in the area Operation of a mechanical exhaust such as an exhaust fan kitchen ventilation system clothes dryer or fireplace may cre ate conditions requiring special attention to avoid unsatisfactory operation of gas appliances...

Page 17: ...usage Follow all notes procedures and required materials in the SEALED COMBUS TION AIR SUPPLY section in these instructions when installing the combustion air pipe from the unit and into a ventilated attic space or crawl space DO NOT terminate vent pipe in an Attic or Crawl Space Ventilated Combustion Air Termination Refer to Figure 22 for required attic termination for the combustion air intake p...

Page 18: ...p pump must be approved for use with acidic condensate CONDENSATE DRAIN TRAP AND DRAIN FREEZE PROTECTION Special precautions MUST be made if installing furnace in an area which may drop below freezing This can cause improper operation or damage to the equipment If the furnace is installed in an area that has the potential of freezing the drain line and the drain trap must be pro tected Use a 3 to ...

Page 19: ...gth x 1 8 0 3 cm diameter tubing 2 pieces of 4 10 cm length x 1 8 0 3 cm diameter tubing 1 5 16 0 8 cm tee 1 5 16 0 8 cm x 1 8 0 3 cm reducing coupling 1 1 8 0 3 cm adapter 1 Dwyer Manometer These items are required in order to properly perform the required star tup procedure IGNITION SYSTEM SEQUENCE 1 Turn the gas supply ON at external valve and main gas valve 2 Set the thermostat above room temp...

Page 20: ...s 3600 then divided by the time it took to measure 0 10 m3 of gas from the gas meter For Propane LP Gas multiply the Heat content of the gas MJ m3 or Default 93 15 times 0 10 m3 of gas measured at the gas meter times a baro metric pressure and temperature correction factor of 0 960 times 3600 then divided by the time it took to measure 0 10 m3 of gas from the gas meter The formula for metric input...

Page 21: ...ll reference atmo spheric pressure Refer to Figure 26 for connection details IMPORTANT The cap for the pressure regulator must be removed entirely to gain access to the adjustment screw Loosening or tightening the cap does not adjust the flow of gas 1 Refer to Figure 25 for location of pressure regulator adjustment cap and adjustment screw on main gas valve 2 Turn gas and electrical supplies on an...

Page 22: ...ws user selection of the blower speed that is energized during continuous fan operation Place jumper on the HI COOL LO COOL or HEAT pins The blower speed connections shown in Figure 27 are typical How ever these connections may vary from model to model and may be changed as needed to give proper heating and cooling airflow WITH BURNER BOX COVER IN PLACE WITH BURNER BOX COVER REMOVED FIGURE 26 Read...

Page 23: ... 35 1175 33 1105 31 1045 30 990 28 905 25 890 25 790 22 80 1600 C 100 1600 C HIGH 1960 56 1955 55 1925 55 1890 54 1830 52 1765 50 1695 48 1615 46 1600 45 1485 42 M HI 1565 44 1560 44 1560 44 1575 45 1545 44 1530 43 1475 42 1425 40 1365 39 1260 36 M LO 1230 35 1275 36 1285 36 1300 37 1310 37 1300 37 1280 36 1245 35 1190 34 1070 30 LOW 930 26 945 27 965 27 975 28 975 28 975 28 975 28 950 27 910 26 8...

Page 24: ... that total system static is 0 58 w c To determine the system airflow complete the follow ing steps Obtain the airflow values at 0 50 w c 125 Pa 0 60 w c 150 Pa ESP Airflow 0 50 2285 CFM 64 70 m3 min Airflow 0 60 2175 CFM 61 59 m3 min Subtract the airflow 0 50 w c 125 Pa from the airflow 0 60 w c 150 Pa to obtain airflow difference 2175 2285 110 CFM 3 11 m3 min Subtract the total system static fro...

Page 25: ...105564 UIM A 0205 Unitary Products Group 25 SECTION XI WIRING DIAGRAM FIGURE 28 Wiring Diagram ...

Page 26: ...105564 UIM A 0205 26 Unitary Products Group NOTES ...

Page 27: ...105564 UIM A 0205 Unitary Products Group 27 NOTES ...

Page 28: ...o change without notice Printed in U S A 105564 UIM A 0205 Copyright by York International Corp 2005 All rights reserved Supersedes 035 20377 002 Rev A 0904 Unitary 5005 Norman Product York OK Group Drive 73069 ...

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