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EXAMPLE: (0 2000 altitude)
Heating value 1050 Bmicu ft
Specific gravity 062
Therefore: Orifice No. 45
Manifold pressure 3 6=in wc
* Furnace is shipped with No. 45 orifices. In this example
all main burner orifices are the correct size and do not need
to be changed to obtain the proper input rate.
Check and verify7 burner orifice size in fhnaace. NEVER ASSUME
ORIFI(E SIZE; ALWAYS CHECK AND VERIFY
2. Adjust maniibld pressure to obtain input rate
NOTE: Manifold pressure must always be measured with burner
enclosure fiont REMOVED Gas meter must always be clocked
with burner enclosure front INSTALLED.
a Remove burner enclosure flout.
b. Remove cap that conceals adjustment screw fk_r gas valve
regulator. (See Fig 46.)
c Jumper R and W thermostat connections on control to start
f_/rnace operation.
d. Turn adjusting screw, counterclockwise (out) to decrease
manifold pressure or clockwise (in) to increase manifbld
pressure
NOTE: This furnace has been approved for a manifold pressure
of 32 in. wc to 3.8 in. wc when installed at ahimdes up to 2000 ft.
For ahimdes above 2000 ft, the manil:bld pressure can be adjusted
from 22 in. wc to 3.8 in. wc. If manifold pressure is outside this
range, change burner orifices to obtain pressure in this range.
tNIT DAMAGE HAZARD
Failure to ibllow this caution may result in reduced furnace
tifc
DO NOT bottom out gas valve regulator adjusting screw
This can result in unregulated manit\_ld pressure and result in
excess overfire and heat exchanger failures.
NOTE: If orifice hole appears damaged or it is suspected to have
been re&illed, check orifice hole with a numbered &ill bit of
correct size. Never re&ill an orifice. A burr=fi'ee and squarely
aligned orifice hole is essential for proper flame characteristics.
e. Replace gas valve regulator adjustment screw cap.
i\ Replace burner enclosure fi'ont and veri/_ adjusted gas
input rate using method outlined in item 3.
[TNTT DAMAGE HAZARD
Failure to follow t_is caution may result in component
damage due to flame impingement of burners and heat
exchangers.
DO NOT re&ill orifices. Improper &illing (burrs. out=of =
round holes, etc.) can cause excessive burner noise and
misdirection of burner flames. (See Fig. 47.)
g. Look through sight glass in burner enclosure and check
burner flame. Burner flame should be clear blue, ahnost
tlansparent. (See Fig. 480
h. Remove jumper fiom R and W.
3. Verii}- natural gas input rate by clocking gas meter.
NOTE: Be sure all pressure robing, cornbustion=air and vent
pipes, and bunaer enclosure front are in place when checking input
by clocking gas meter.
43
\
%
BURNER
---- ORIFICE
Fig. 47--Burner Orifice
A93059
a. Calculate high-altitude adjustment (if required).
United States
At altitudes above 2000 R, this Nrnace has been approved for a 2%
&rate for each 1000 R above sea level. See Table 12 ibr &rate
multiplier ihctor.
EXAMPLE: 100,000 Btuh input furnace installed at 4300 ft.
Furnace input Rate Derate Furnace Input Rate
at Sea Level X Multiplier = at Installation
Factor Altitude
100,000 X 0.91 = 91,000
Canada
At installation altitudes fiom 200! to 4500 it, this _:_/macemust be
&rated 5% by an aud_orized Gas (;onve*sion Station. To deter-
mine con'ect input rate for ahimd< see example above and use
095 as derate multiplier fhctor.
b Reinstall burner box cover.
c. Gas valve regulator seal cap MUST be installed
d Turn off all other gas appliances and pilots.
e Start furnace and let operate for 3 minutes
i_ Measure time (in sec) ibr gas meter test dial to complete 1
revolution
g. Reibr to Table 13 %r cuft of gas per hr.
h. Multiply gas rate (cu flihr) X heating value (Bmicu it)
using natural gas heating value from local gas
utility/supplier
Table 12--Ntitude Derate MuNplier for U.S.A.
ALTITUDE
{FT}
0--2000
2001--3000
3001--4000
4001--5000
8001--6000
6001--7000
7001--8000
8001--9000
9001--10,000
* Derate multiplierfactoris
% OF DI=RATE MULTiPLiER
BERATE FACTOR FOR U.S.A*
0 1.00
4--6 0.95
6--8 0.93
8--10 0.91
10--12 0.89
12--14 0.87
14--16 0.85
16--18 0.83
18--20 0.81
based on midpoint altitude for altitude range.
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