Caution; Gas Piping - Lennox MERIT ML180UH Installation Instructions Manual

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.
Nominal
Internal
Iron Pipe
Diameter
Size
inches
inches
(mm)
(3.048)
(mm)
1/2 .622 172
(12.7) (17.799) (4.87)
3/4 .824 360
(19.05) (20.930) (10.19)
1 1.049 678
(25.4) (26.645) (19.19)
1−1/4 1.380 1350
(31.75) (35.052) (38.22)
1−1/2 1.610 2090
(38.1) (40.894) (59.18)
2 2.067 4020
(50.8) (52.502) (113.83)
2−1/2 2.469 6400
(63.5) (67.713) (181.22)
3 3.068 11300
(76.2) (77.927) (319.98)
NOTE − Capacity given in cubic feet (m
Gas Pipe Capacity − ft
10 20 30
(6.096) (9.144)
118 95
(3.34) (2.69)
247 199
(7.00) (5.63)
466 374
(13.19) (10.59)
957 768
(27.09) (22.25)
1430 1150
(40.49) (32.56)
2760 2220
(78.15) (62.86)
4400 3530
(124.59) (99.95)
7780 6250
(220.30) (176.98)
3
) of gas per hour and based on 0.60 specific gravity gas.
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.
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
3 3
/hr (m /hr)
Length of Pipe − feet (m)
40 50 60
(12.192) (15.240) (18.288)
81 72 65
(2.29) (2.03) (1.84)
170 151 137
(4.81) (4.28) (3.87)
320 284 257
(9.06) (8.04) (7.27)
657 583 528
(18.60) (16.50) (14.95)
985 873 791
(27.89) (24.72) (22.39)
1900 1680 1520
(53.80) (47.57) (43.04)
3020 2680 2480
(85.51) (75.88) (70.22)
5350 4740 4290
(151.49) (134.22) (121.47)
Page 23
IMPORTANT
70 80 90
(21.336) (24.384) (27.432)
60 56 52
(1.69) (1.58) (1.47)
126 117 110
(3.56) (3.31) (3.11)
237 220 207
(6.71) (6.23) (5.86)
486 452 424
(13.76) (12.79) (12.00)
728 677 635
(20.61) (19.17) (17.98)
1400 1300 1220
(39.64) (36.81) (34.55)
2230 2080 1950
(63.14) (58.89) (55.22)
3950 3670 3450
(111.85) (103.92) (97.69)
100
(30.480)
50
(1.42)
104
(2.94)
195
(5.52)
400
(11.33)
600
(17.00)
1160
(32.844)
1840
(52.10)
3260
(92.31)