Gas Rate Cubic Feet Per Hour; Gas Heat Stages - York ZJ078 Installation Manual

524581-YIM-I-0512
Table 26: Gas Rate Cubic Feet Per Hour
Seconds for
One Rev.
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
50
52
54
56
58
60
NOTE: To find the Btu input, multiply the number of cubic feet
of gas consumed per hour by the Btu content of the gas
in your particular locality (contact your gas company for
this information as it varies widely from area to area).
EXAMPLE
By actual measurement, it takes 19 seconds for the hand on a 1
cubic foot dial to make a revolution with a 192,000 Btuh furnace
running. To determine rotations per minute, divide 60 by 19 =
3.16. To calculate rotations per hour, multiply 3.16  60 = 189.6.
Multiply 189.6  1 (0.5 if using a 1/2 cubic foot dial) = 189.6.
Multiply 189.6  (the Btu rating of the gas). For this example,
assume the gas has a Btu rating of 1050 Btu/ft.
199,000 Btuh is within 5% of the 192,000 Btuh rating of the
furnace.
58
Size of Test Dial
1/2 cu. ft. 1 cu. ft.
180 360
150 300
129 257
113 225
100 200
90 180
82 164
75 150
69 138
64 129
60 120
56 113
53 106
50 100
47 95
45 90
43 86
41 82
39 78
37 75
36 72
35 69
34 67
32 64
31 62
30 60
3
. The result of
Manifold Gas Pressure Adjustment
This gas furnace has two heat stages. Therefore, the gas valve
has two adjustment screws located under a plastic protective
cover. The second stage (100% input) adjustment screw is
adjacent to the "HI" marking on the valve and the first stage
(60% input) adjustment screw is located adjacent to the "LO"
marking on the valve (See Figure 35).
Manifold pressure adjustment procedure.
Adjust second stage (100% input) pressure first, then adjust
first stage (60% input) pressure.
1. Turn off all power to the unit.
2. Using the outlet pressure port on the gas valve, connect a
manometer to monitor the manifold pressure.
3. Remove plastic cap covering HI and LO pressure
adjustment screws.
4. Turn on power to the unit.
5. Set thermostat to call for second stage heat and start
furnace.
6. If necessary, using a screwdriver, turn the second stage
adjustment screw (adjacent to the "HI" marking on the
valve) clockwise to increase manifold pressure or
counterclockwise to decrease manifold pressure. Be sure
not to over-fire the unit on second stage.
7. After the high manifold pressure has been checked, adjust
the thermostat to call for first stage heat.
8. If necessary, using a screwdriver, turn the first stage
adjustment screw (adjacent to the "LO" marking on the
valve) clockwise to increase manifold pressure or
counterclockwise to decrease manifold pressure. Be sure
not to under-fire the unit on first stage.
9. Once pressure has been checked, replace the plastic cap
covering the HI and LO pressure adjustment screws.
NOTE: When using natural gas, the manifold pressure for
second stage (100% input) should be 3.5 IWG ± 0.3.
The manifold pressure for first stage (60% input) when
using natural gas should be 1.5 IWG ± 0.3.
Table 27: Gas Heat Stages
# of Burner Tubes
4
6
8
2nd Stage Input 1st Stage Input
(100% Btuh) (60% Btuh)
120,000 72,000
180,000 108,000
240,000 144,000
Johnson Controls Unitary Products