Operating instructions
NOTE: This furnace has been approved for a manifold pressure
of 3.2 in. wc to 3.8 in. wc when installed at altitudes up to 2000 ft.
For altitudes above 2000 ft, the manifold pressure can be adjusted
from 2.0 in. wc to 3.8 in. wc. If manifold pressure is outside this
range, change burner orifices to obtain pressure in this range.
CAUTION: 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.
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.
CAUTION: 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 burners and heat exchang-
ers causing failures. (See Fig. 58.)
e. Replace gas valve regulator adjustment screw cap.
f. Replace burner enclosure front and verify adjusted gas
input rate using method outlined in item 3.
TABLE 9—MODEL 350MAV ORIFICE SIZE AND MANIFOLD PRESSURE FOR CORRECT INPUT
FOR USE WITH 040 THROUGH 120 SIZE FURNACES ONLY
(TABULATED DATA BASED ON 20,000 BTUH PER BURNER, DERATED 2 PERCENT FOR EACH 1000 FT ABOVE SEA LEVEL)
ALTITUDE
RANGE
(FT)
AVG GAS
HEAT VALUE
(BTU/CU FT)
SPECIFIC GRAVITY OF NATURAL GAS
0.58 0.60 0.62 0.64 0.66
Orifice
no.
Manifold
Pressure
Orifice
no.
Manifold
Pressure
Orifice
no.
Manifold
Pressure
Orifice
no.
Manifold
Pressure
Orifice
no.
Manifold
Pressure
U.S.A. and Canada
0
to
2000
0%
derate
850 43 3.7 43 3.8 42 3.2 42 3.3 42 3.4
875 43 3.5 43 3.6 43 3.7 43 3.8 42 3.2
900 44 3.7 43 3.4 43 3.5 43 3.6 43 3.7
925 44 3.5 44 3.7 44 3.8 43 3.4 43 3.5
950 44 3.4 44 3.5 44 3.6 44 3.7 44 3.8
975 44 3.2 44 3.3 44 3.4 44 3.5 44 3.6
1000 45 3.7 45 3.8 44 3.2 44 3.4 44 3.5
1025 45 3.5 45 3.6 45 3.7 44 3.2 44 3.3
1050 45 3.3 45 3.4 45 3.6 45 3.7 45 3.8
1075 45 3.2 45 3.3 45 3.4 45 3.5 45 3.6
1100 47 3.6 47 3.7 45 3.2 45 3.4 45 3.5
ALTITUDE
RANGE
(FT)
AVG GAS
HEAT VALUE
(BTU/CU FT)
SPECIFIC GRAVITY OF NATURAL GAS
0.58 0.60 0.62 0.64 0.66
Orifice
no.
Manifold
Pressure
Orifice
no.
Manifold
Pressure
Orifice
no.
Manifold
Pressure
Orifice
no.
Manifold
Pressure
Orifice
no.
Manifold
Pressure
U.S.A. and Canada
Altitudes
2001
to
3000
or
Canada
Altitudes
2001
to
4500
5%
derate
775 43 3.8 42 3.2 42 3.3 42 3.4 42 3.5
800 43 3.5 43 3.7 43 3.8 42 3.2 42 3.3
825 44 3.8 43 3.4 43 3.6 43 3.7 43 3.8
850 44 3.6 44 3.7 44 3.8 43 3.5 43 3.6
875 44 3.4 44 3.5 44 3.6 44 3.7 43 3.4
900 44 3.2 44 3.3 44 3.4 44 3.5 44 3.6
925 45 3.7 45 3.8 44 3.2 44 3.3 44 3.4
950 45 3.5 45 3.6 45 3.7 45 3.8 44 3.3
975 45 3.3 45 3.4 45 3.5 45 3.6 45 3.8
1000 45 3.1 45 3.2 45 3.4 45 3.5 45 3.6
1025 45 3.0 45 3.1 45 3.2 45 3.3 45 3.4
ALTITUDE
RANGE
(FT)
AVG GAS
HEAT VALUE
(BTU/CU FT)
SPECIFIC GRAVITY OF NATURAL GAS
0.58 0.60 0.62 0.64 0.66
Orifice
no.
Manifold
Pressure
Orifice
no.
Manifold
Pressure
Orifice
no.
Manifold
Pressure
Orifice
no.
Manifold
Pressure
Orifice
no.
Manifold
Pressure
U.S.A. Only
3001
to
4000
7%
derate
750 43 3.7 43 3.8 42 3.3 42 3.4 42 3.5
775 43 3.5 43 3.6 43 3.7 43 3.8 42 3.2
800 44 3.7 43 3.4 43 3.5 43 3.6 43 3.7
825 44 3.5 44 3.6 44 3.8 43 3.4 43 3.5
850 44 3.3 44 3.4 44 3.5 44 3.7 44 3.8
875 45 3.8 44 3.2 44 3.3 44 3.5 44 3.6
900 45 3.6 45 3.7 45 3.8 44 3.3 44 3.4
925 45 3.4 45 3.5 45 3.6 45 3.7 44 3.2
950 45 3.2 45 3.3 45 3.4 45 3.5 45 3.7
975 45 3.0 45 3.2 45 3.3 45 3.4 45 3.5
1000 45 2.9 45 3.0 45 3.1 45 3.2 45 3.3
* Orifice numbers 45 are factory installed.
Percents of derate are based on midpoints of U.S. altitude ranges.
—41—