44
SETTING INPUT RATE
The furnace is shipped from the factory with #42 orifices.
They are sized for natural gas having a heating value of
1050 BTU/cu. ft. and a specific gravity of .60.
Since heating values vary geo-graphically, the manifold
pressure and/or gas orifice size may need to be changed
to adjust the furnace to its nameplate input. Consult the
local gas utility to obtain the yearly average heating value
and orifice size required to fire each individual burner at
25,000 BTU/HR.
NOTE: Refer to the High Altitude Section of this manual
and the National Fuel Gas Code for high altitude rate ad-
justment above 2,000 ft.
TIMING DIAGRAM, FIELD SELECTIONS &
ADJUSTMENTS
Field Selections
TABLE 11
METER TIME
METER TIME IN MINUTES AND SECONDS FOR NORMAL INPUT RATING OF FURNACES EQUIPPED FOR NATURAL
GAS OR L.P.
INPUT
(BTU/HR)
50,000
75,000
100,000
125,000
150,000
ONE
TEN
ONE
TEN
ONE
TEN
ONE
TEN
ONE
TEN
Formula: Input BTU/HR =
Heating Value of Gas (BTU/ft
3
) × 3600 x correction factor
Formula: Input BTU/HR = Time (in seconds) for 1 cubic ft of Gas
METER SIZE
(FT
3
/REV)
HEATING VALUE OF GAS (BTU/FT
3
)
900 1000 1040 1100 2500
MIN SEC MIN SEC MIN SEC MIN SEC MIN SEC
1 5 1 12 1 15 1 19 3 0
10 48 12 0 12 29 13 12 30 0
0 43 0 48 0 50 0 53 2 0
7 12 8 0 8 19 8 48 20 0
0 32 0 36 0 37 0 40 1 30
5 24 6 0 6 14 6 36 15 0
0 26 0 29 0 30 0 32 1 12
4 19 4 48 4 60 5 17 12 0
0 22 0 24 0 25 0 26 1 0
3 36 4 0 4 10 4 24 10 0
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