Lenox Lennox Merit Series Gas Furnace Upflow/Horizontal air discharge, ML180UHE Gas Piping

Page 23

Gas Piping

Gas supply piping should not allow more than 0.5"W.C. drop

in pressure between gas meter and unit. Supply gas pipe

must not be smaller than unit gas connection.

CAUTION

If a flexible gas connector is required or allowed by

the authority that has jurisdiction, black iron pipe

shall be installed at the gas valve and extend outside

the furnace cabinet. The flexible connector can then

be added between the black iron pipe and the gas

supply line.

Gas Supply

1 − This unit is shipped standard for left or right side instal-

lation of gas piping (or top entry in horizontal applica-

tions). Connect the gas supply to the piping assembly.

2 − When connecting the gas supply piping, consider fac-

tors such as length of run, number of fittings, and fur-

nace rating to avoid excessive pressure drop. Table 9

lists recommended pipe sizes for typical applications.

3 − The gas piping must not run in or through air ducts,

clothes chutes, gas vents or chimneys, dumb waiters,

or elevator shafts.

4 − The piping should be sloped 1/4 inch (6.4 mm) per 15

feet (4.57 m) upward toward the meter from the fur-

nace. The piping must be supported at proper intervals

[every 8 to 10 feet (2.44 to 3.01 m)] with suitable hang-

ers or straps. Install a drip leg in vertical pipe runs to the

unit.

5 − A 1/8" N.P.T. plugged tap or pressure post is located

on the gas valve to facilitate test gauge connection.

See figure 35.

6 − In some localities, codes may require the installation of

a manual main shut-off valve and union (furnished by

the installer) external to the unit. The union must be of

the ground joint type.

IMPORTANT

Compounds used on threaded joints of gas piping

must be resistant to the actions of liquified petro-

leum gases.

NOTE − If emergency shutoff is necessary, shut off the main

manual gas valve and disconnect main power to the fur-

nace. The installer should properly label these devices.

TABLE 9

Gas Pipe Capacity − ft3/hr (m3/hr)

Nominal

Iron Pipe

Size

inches

(mm)

Internal

Diameter

inches

(mm)

Length of Pipe − feet (m)

(3.048)

(6.096)

(9.144)

(12.192)

(15.240)

(18.288)

(21.336)

(24.384)

(27.432)

100

(30.480)

1/2

(12.7)

.622

(17.799)

172

(4.87)

118

(3.34)

(2.69)

(2.29)

(2.03)

(1.84)

(1.69)

(1.58)

(1.47)

(1.42)

3/4

(19.05)

.824

(20.930)

360

(10.19)

247

(7.00)

199

(5.63)

170

(4.81)

151

(4.28)

137

(3.87)

126

(3.56)

117

(3.31)

110

(3.11)

104

(2.94)

(25.4)

1.049

(26.645)

678

(19.19)

466

(13.19)

374

(10.59)

320

(9.06)

284

(8.04)

257

(7.27)

237

(6.71)

220

(6.23)

207

(5.86)

195

(5.52)

1−1/4

(31.75)

1.380

(35.052)

1350

(38.22)

957

(27.09)

768

(22.25)

657

(18.60)

583

(16.50)

528

(14.95)

486

(13.76)

452

(12.79)

424

(12.00)

400

(11.33)

1−1/2

(38.1)

1.610

(40.894)

2090

(59.18)

1430

(40.49)

1150

(32.56)

985

(27.89)

873

(24.72)

791

(22.39)

728

(20.61)

677

(19.17)

635

(17.98)

600

(17.00)

(50.8)

2.067

(52.502)

4020

(113.83)

2760

(78.15)

2220

(62.86)

1900

(53.80)

1680

(47.57)

1520

(43.04)

1400

(39.64)

1300

(36.81)

1220

(34.55)

1160

(32.844)

2−1/2

(63.5)

2.469

(67.713)

6400

(181.22)

4400

(124.59)

3530

(99.95)

3020

(85.51)

2680

(75.88)

2480

(70.22)

2230

(63.14)

2080

(58.89)

1950

(55.22)

1840

(52.10)

(76.2)

3.068

(77.927)

11300

(319.98)

7780

(220.30)

6250

(176.98)

5350

(151.49)

4740

(134.22)

4290

(121.47)

3950

(111.85)

3670

(103.92)

3450

(97.69)

3260

(92.31)