SERVICE AND TECHNICAL SUPPORT MANUAL
Gas Furnace: N9MSB
Specifications subject to change without notice.
440 04 4413 03
11
Table 3 (CONT.)
Orifice Size and Manifold Pressure (in. w.c.) for Gas Input Rate
−
Single Stage
A11253B
S
A
G
L
A
R
U
T
A
N
F
O
Y
T
I
V
A
R
G
C
I
F
I
C
E
P
S
S
A
G
.
G
V
A
HEAT VALUE
0.58
0.60
0.62
0.64
AT ALTITUDE
Orifice
Manifold
Orifice
Manifold
Orifice
Manifold
Orifice
Manifold
(Btu/cu ft)
No.
Pressure
No.
Pressure
No.
Pressure
No.
Pressure
ALTITUDE
RANGE
ft (m)
SINGLE-STAGE FURNACE
(TABULATED DATA BASED ON 20,000 BTUH PER BURNER, DERATED 2%/1000 FT (305M) ABOVE SEA LEVEL)
650
42
3.4
42
3.5
42
3.6
42
3.7
7001
675
43
3.8
42
3.2
42
3.3
42
3.4
(2134)
700
43
3.5
43
3.7
43
3.8
42
3.2
725
44
3.8
43
3.4
43
3.5
43
3.6
750
44
3.5
44
3.7
44
3.8
43
3.4
8000
775
44
3.3
44
3.4
44
3.5
44
3.7
(2438)
800
44
3.1
44
3.2
44
3.3
44
3.4
825
44
2.9
44
3.0
44
3.1
44
3.2
625
42
3.4
42
3.5
42
3.6
42
3.7
8001
650
43
3.8
42
3.2
42
3.3
42
3.4
(2439)
675
43
3.5
43
3.6
43
3.7
42
3.2
700
44
3.7
43
3.4
43
3.5
43
3.6
725
44
3.5
44
3.6
44
3.7
44
3.8
9000
750
44
3.3
44
3.4
44
3.5
44
3.6
(2743)
775
44
3.0
44
3.2
44
3.3
44
3.4
9001
600
42
3.3
42
3.4
42
3.6
42
3.7
(2744)
625
43
3.7
42
3.2
42
3.3
42
3.4
650
43
3.5
43
3.6
43
3.7
43
3.8
675
44
3.7
44
3.8
43
3.4
43
3.5
10000
700
44
3.4
44
3.5
44
3.7
44
3.8
(3048)
725
44
3.2
44
3.3
44
3.4
44
3.5
* Orifice numbers shown in
BOLD
are factory-installed.
to
to
to
U.
S
.A.
On
ly
U.
S
.A.
On
ly
U.
S
.A.
On
ly
Adjust Temperature Rise
NOTE
: Blower door must be installed when taking temperature
rise reading. Leaving blower door off will result in incorrect
temperature measurements, due to possible changes in duct
static pressure and airflow.
FURNACE DAMAGE HAZARD
Failure to follow this caution may result in:
S
Overheating the heat exchangers or condensing
flue gases in heat exchanger areas not designed
for condensate.
S
Shortened furnace life.
S
Component damage.
Temperature rise must be within limits specified on furnace
rating plate. Recommended operation is at midpoint of rise
range or slightly above.
CAUTION
!
Jumper R to W to check gas-heat temperature rise. Do not
exceed temperature rise ranges specified on unit rating plate.
This furnace must operate within the temperature rise ranges
specified on the furnace rating plate. Determine the air
temperature as follows:
1. Place duct thermometers in return and supply ducts as
close to furnace as possible. Be sure thermometers do
not “see” heat exchangers so that radiant heat does not
affect thermometer readings. This is particularly
important with straight
−
run ducts.
2. When thermometer readings stabilize, subtract return
−
air
temperature from supply
−
air temperature to determine
temperature rise.
If the temperature rise is outside this range, check the
following:
1. Gas input rate.
2. Derate for altitude if applicable.
3. Return and supply ducts for excessive restrictions
causing static pressures greater than 0.50
−
in. w.c. (125
Pa)
4. Adjust temperature rise by adjusting blower speed.
S
Increase blower speed to reduce temperature rise.
S
Decrease blower speed to increase temperature rise.
ELECTRICAL OPERATION HAZARD
Failure to follow this warning could result in personal injury
or death.
Disconnect 115vac electrical power before changing speed
tap.
!
WARNING
