Iv-Heating System Service Checks - Lennox G27M series Unit Information

IV–HEATING SYSTEM SERVICE CHECKS
A–A.G.A. / C.G.A. Certification
All G27M units are A.G.A. / C.G.A. design certified with-
out modifications. Refer to the G27M Installation
Instruction for Information.
B–Gas Piping
Gas supply piping should not allow more than 0.5"W.C.
drop in pressure from unit with gas valve off and with
unit operating at second–stage heat (high fire). Supply
gas pipe must not be smaller than unit gas connection.
Refer to table 6 if pressure drop exceeds 0.5"W.C. or if
gas piping is suspect. Do not operate furnace below
nameplate minimum line pressure.
C–Testing Gas Piping
IMPORTANT
In case emergency shutdown is required, turn off
the main shut-off valve and disconnect the main
power to unit. These controls should be properly
labeled by the installer.
When pressure testing gas lines, the gas valve must be
disconnected and isolated. Gas valves can be damaged
if subjected to more than 0.5psig (14" W.C.). See figure
16 . If the pressure is equal to or less than 0.5psig
(14"W.C.), use the manual shut–off valve before
pressure testing to isolate furnace from gas supply.
Nominal Internal
Iron Pipe Size I Pi Si Di Diameter
–Inches(mm) –Inches(mm)
1/4 .364
(6.35) (9.246)
3/8 .493
(9.53) (12.522)
1/2 .622
(12.7) (17.799)
3/4 .824
(19.05) (20.930)
1 1.049
(25.4) (26.645)
1–1/4 1.380
(31.75) (35.052)
1–1/2 1.610
(38.1) (40.894)
2 2.067
(50.8) (52.502)
2–1/2 2.469
(63.5) (67.713)
3 3.068
(76.2) (77.927)
4 4.026
(101.6) (102.260)
NOTE–Capacity given in cubic feet of gas per hour (kilo liters of gas per hour) and based on 0.60 specific gravity gas.
TABLE 6
GAS PIPE CAPACITY – FT
10 20 30
(3.048) (6.096) (9.144)
43 29 24
(1.13) (.82) (.68)
95 65 52
(2.69) (1.84) (1.47)
175 120 97
(4.96) (3.40) (2.75)
360 250 200
(10.19) (7.08) (5.66)
680 465 375
(919.25) (13.17) (10.62)
1400 950 770
(39.64) (26.90) (21.80)
2100 460 1180
(59.46) (41.34) (33.41)
3950 2750 2200
(111.85) (77.87) (62.30)
6300 4350 3520
(178.39) (123.17) (99.67)
11000 7700 6250
(311.48) (218.03) (176.98)
23000 15800 12800
(651.27) (447.39) (362.44)
Page 12
GAS PIPING TEST PROCEDURE
MANUAL MAIN SHUT–OFF VALVE
GAS VALVE WILL NOT HOLD TEST
PRESSURE IN EXCESS OF 0.5
PSIG (14"W.C.)
GAS VALVE
When checking piping connections for gas leaks, use
preferred means. Kitchen detergents can cause harmful
corrosion on various metals used in gas piping. Use of a
specialty gas leak detector is strongly recommended. It
is available through Lennox under part number
31B2001. See Corp. 8411–L10, for further details.
Do not use matches, candles, flame or any other source
of ignition to check for gas leaks.
D–Testing Gas Supply Pressure
When testing supply gas pressure, connect test gauge to
inlet pressure tap (field provided). See figure 16. Check
gas line pressure with unit firing at maximum rate. Low
pressure may result in erratic operation or underfire. High
pressure can result in permanent damage to gas valve or
overfire. For natural gas units, operating pressure at unit
gas connection must be a minimum of 5.0" W.C. but no
more than 13.0"W.C. at any time.
3 /HR (kL/HR)
Length of Pipe–Feet(m)
40 50 60
(12.192) (15.240) (18.288)
20 18 16
(.57) (.51) (.45)
45 40 36
(1.27) (1.13) (1.02)
82 73 66
(2.32) (2.07) (1.87)
170 151 138
(4.81) (4.28) (3.91)
320 285 260
(9.06) (8.07) (7.36)
660 580 530
(18.69) (16.42) (15.01)
990 900 810
(28.03) (25.48) (22.94)
1900 1680 1520
(53.80) (47.57) (43.04)
3000 2650 2400
(84.95) (75.04) (67.96)
5300 4750 4300
(150.07) (134.50) (121.76)
10900 9700 8800
(308.64) (274.67) (249.18)
CAP
FIELD PROVIDED
LINE PRESSURE TAP
FIGURE 16
70 80 90
(21.336) (24.384) (27.432)
15 14 13
(.42) (.40) (.37)
33 31 29
(.73) (.88) (.82)
61 57 53
(1.73) (1.61) (1.50)
125 118 110
(3.54) (3.34) (3.11)
240 220 205
(6.80) (6.23) (5.80)
490 460 430
(13.87) (13.03) (12.18)
750 690 650
(21.24) (19.54) (18.41)
1400 1300 1220
(39.64) (36.81) (34.55)
2250 2050 1950
(63.71) (58.05) (55.22)
3900 3700 3450
(110.43) (104.77) (97.69)
8100 7500 7200
(229.36) (212.37) (203.88)
100
(30.480)
12
(.34)
27
(.76)
50
(1.42)
103
(2.92)
195
(5.52)
400
(11.33)
620
(17.56)
1150
(32.56)
1850
(52.38)
3250
(92.03)
6700
(189.72)