I
AIR FLOW
The importance of proper air flow
over the heat exchanger cannot be
over emphasized. One of the most
common causes of heat exchanger
failure is overheating due to low air
flow An air flow table is located
inside the blower door.
Temperature Rise Check. To
determine if the air flow is correct,
make a temperature rise check.
1. Insert a thermometer in the
supply air duct as close to the
furnace as possible yet out of a
direct line from the heat
exchanger.
2. Insert a thermometer in the
return air duct as close to the
furnace as possible.
3. Operate the furnace.
4. When the thermometer in the
supply air duct stops rising
(approximately 5 minutes),
subtract the return air
temperature from the supply air
temperature. The difference is
the temperature rise.
5. Compare the measured
temperature rise to the approved
temperature rise range listed on
the furnace name plate.
If the measured temperature rise is
above the approved range, the air
flow is too low. More air must be
moved either by speeding up the
blower, removing restrictions in the
duct system, or by adding more
supply or return air duct. If the
measured temperature rise is below
the approved range, the air flow is
too much. Use a lower speed tap on
the multi-speed blower.
Ideally the measured temperature
rise should be in the middle of the
range.
---+-+--~~
FIGURE 68
TEMPERATURE RISE MEASUREMENT
FIGURE 69
FURNACE NAME PLATE
AIR COt«llTIONINC OIUISION
FORT SMITH,
~
DIRECT \'ENT OR NON DIRECT VE!loT
FORCED AIR FURNACE FOR INDOOR INSTALLATION
OSI.YIN BUll.DING CONSTRUCI"ED ON SITE
ELECl1llC 115V.60HZ.1-PIL, MAX TOTAL INPUr 6. 3 AMPS
MAXIMUM OVER CURRENT PROTECTION 1.5AMPERES.
MODEL NO.
( - >GRA-07El1AES
INPUT BTIJ/HR.
75, 000
l.lMITSin"llNG
220
AUX. LIMIT SETTING
IIAXJMUM OAS SUP9'LY PRESSURE TO FUANACe
IIIINIMUM OA8 IUPPL Y PRESSURE FOR PURPOSES
OF INPUT ADIUSTlll!NT TO flURNACE
~PRH8UIIE
ro11TEMPERATIJJtEIUSl!OF 45
SERIAL NUMBER
OC50702 F1894 0080
ECUIPPal FOR USEwm<
NATURAL GAS
NAT. LP.
7•
14-W.C.
11·w.c.
10-W.C.
•r.ro 75 •r
MAX.EXT.STATIC PRESSl.l!E BLOWER MOTOR MIN. H.P .
. 12 INCHESW.C. 11-7 1/2
. 58
INCHESW.C. 11-7 1/2
nus IS A CATEGORY IV FORCED AIR FURNACE WHE.'1 USING INDOOR AIR FOR COl\mUSTION.
THIS IS A CA TF,GORY IV TYPE ~'SP DIRECT VE1'T FORCED Alli FCIINACE WHEN l!SING OUTDOOR
AIR FOR COMBUSTION
61
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