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Adjustments
WARNING
!
FIRE HAZARD
Failure to follow this warning could result in personal
injury, death and/or property damage.
DO NOT bottom out gas valve regulator adjusting screw.
This can result in unregulated manifold pressure and result
in excess overfire and heat exchanger failures.
CAUTION
!
FURNACE DAMAGE HAZARD
Failure to follow this caution may result in reduced furnace
life.
DO NOT redrill orifices. Improper drilling (burrs,
out- -of- -round holes, etc.) can cause excessive burner noise
and misdirection of burner flames. This can result in flame
impingement of heat exchangers, causing failures. (See Fig.
50.)
Furnace gas input rate on rating plate is for installations at
altitudes up to 2000 Ft. (610 M). Furnace input rate must be
within +/- -2 percent of furnace rating plate input. For altitudes
above 5500 Ft. (1676 M), a field- -supplied high altitude pressure
switch is required.
1. Determine the correct gas input rate.
The input rating for altitudes above 2,000 ft. (610 M) must
be reduced by 4 percent for each 1,000 ft. (305 M) above
sea level.
For installations below 2000 Ft. (610 M), refer to the unit
rating plate. For installations above 2000 Ft. (610 M),
multiply the input on the rating plate by the de- -rate multi-
plier in Table 9 for the correct input rate.
2. Determine the correct orifice and manifold pressure adjust-
ment. All models in all positions use Table 11 (22,000
Btuh per burner.) See input listed on rating plate.
a. Obtain average yearly gas heat value (at installed alti-
tude) from local gas supplier.
Fig. 54 - - Service Label
b. Obtain average yearly gas specific gravity from local
gas supplier.
c. Find installation altitude in Table 11.
d. Find closest natural gas heat value and specific gravity
in Table 11.
e. Follow heat value and specific gravity lines to point of
intersection to find orifice size and low- -and high- -heat
manifold pressure settings for proper operation.
f. Check and verify burner orifice size in furnace.
NEVER ASSUME ORIFICE SIZE. ALWAYS
CHECK AND VERIFY.
NOTE: If orifice hole appears damaged or it is suspected to have
been redrilled, check orifice hole with a numbered drill bit of
correct size. Never redrill an orifice. A burr- -free and squarely
aligned orifice hole is essential for proper flame characteristics.
g. Replace orifice with correct size, if required by Table
11. Use only factory- -supplied orifices. See
EXAMPLE 1.
Table 9 – Altitude Derate Multiplier for U.S.A.
ALTITUDE
FT. (M)
0–2000
(0--- 610)
2001–3000
(610--- 914)
3001–4000
(914--- 1219)
4001–5000
(1219--- 1524)
5001–6000
1524--- 1829)
6001–7000
(1829--- 2134)
7001–8000
(2134--- 2438)
8001–9000
(2438--- 2743)
9001–10,000
(2743--- 3048)
37
PERCENT
DERATE MULTIPLIER
OF DERATE
FACTOR*
0
1.00
8–12
0.90
12–16
0.86
16–20
0.82
20–24
0.78
24–28
0.74
28–32
0.70
32–36
0.66
36–40
0.62
A190047
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