Bard Bayrd Furnace 403293A - Manual (Page 31)

sicTiON aa — orifici sizi .
See Figure 33 for initial gas orifice sizes as shipped from
factory.
Initial Orifice Size
Mnput Natural Gas Propane
BTU/HR ^Orifice Size Orifice Size
All size units 2.15mm 1.30mm
*See furnace rating plate located on blower door.
FIGURE 33
Check with your local gas supplier to determine heat value
(BTU/CU.FT.) of gas in your area. Depending on your local
heat value and elevation, you may need to adjust manifold
pressure or change orifices to get proper gas input rate.
See Section 23.
SICTION as — DERATINO FOR HIGH
AiTirUDES.
Equipment Needed: Save time by getting these tools before
you start: ttem number(s) 3,7 and 23 listed in Section 10.
A. Installer responsibility.
For operation at elevations above 2,000 feet the den-
sity of air is reduced, therefore, the furnace should be
derated at the rate of four percent (4%) for aactl 1 >000
feet above sea level. It is the Installers' responsibility
to see that the input is adjusted properly.
if the gas supplier has not already derated the gas
BTU value, derating must be achieved by reducing the
size of the main burner orifices. See Table 34 and 35
for proper sizing. Contact gas supplier for more infor­
mation.
Adjustment of the manifold pressure to a lower pres­
sure reading than what is specified in Section 20,
Manifold Pressure Adjustment of this manual is con­
sidered to be an improper derate procedure. With a
lower density of air and a lower manifold pressure at
the burner orifice, the orifice will not aspirate the proper
amount of primary air into the burner. Insufficient pri­
mary air can cause incomplete combustion, yellow tip­
ping and quite possibly carbon build-up.
B. New orifice size.
See appropriate chart below to determine new orifice
size.
To accomplish altitude derate, a natural gas orifice kit
containing the natural gas orifices indicated in Figure
34 is available through your supplier. A similar propane
(LP) gas orifice kit is available. Individual orifices are
also available in a convenient lot size. Use only these
orifices to assure proper performance.
NATURAL GAS-ORIFICE SIZE CHART
Elevation
Gas Up to 2001 3001 4001 5001 6001 7001 8001 9001
Heat^ to to to to to to to to to
Value 2000 3000 4000 5000 6000 7000 8000 9000 10000
BTU/CU.FT. Feet Feet Feet Feet Feet Feet Feet Feet Feet
800-849
850-899
900-949
950-999
1000-1049
1050-1100
2.25mm
2.20mm
2.15mm
2.10mm
2.20mm
2.15mm
2.10mm
2.05mm
2.20mm
2.15mm
2.10mm
2.05mm
2.00mm
2.20mm
2.15mm
2.05mm
2.05mm
2.20
2.15mm
2.10mm
2.05mm
2.20mm
2.10mm
2.05mm
2.00mm
2.00mm
1.90mm
2.15mm
2.10mm
2.05mm
2.10mm
2.05mm
2.05mm
185mm
*At standard conditions: 30:0 inches Mercury, 60*’F, Saturated.
NOTE: Shaded orifices above are not included in natural gas orifice kit. They are available separately.
FIGURE 34
PROPANE (LP) GAS—ORIFICE SIZE CHART
Elevation
Gas Up to 2001 3001 4001 5001 6001 7001 8001 9001
Heat* to to to to to to to to to
Value 2000 3000 4000 5000 6000 7000 8000 9000 10000
BTU/CU.FT. Feet Feet Feet Feet Feet Feet Feet Feet Feet
40,000-140,000 1.30mm 1.25mm 1.25mm 1.20mm 1.20mm 1.20mm 1.15mm 1.15mm 1.10mm
FIGURE 35
NOTE; All orifices above are included in propane (LP) gas orifice kit,
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