Table of Contents
Advertisement
a. Obtain average yearly gas heat value (at installed alti-
tude) from local gas supplier.
b. Obtain average yearly gas specific gravity from local
gas supplier.
c. Find installation altitude in Table 11.
d. Find closest natural gas heat value and specific gravity
in Table 11.
e. Follow heat value and specific gravity lines to point of
intersection to find orifice size and manifold pressure
settings for proper operation.
f. Check and verify burner orifice size in furnace. NEV-
ER ASSUME ORIFICE SIZE. ALWAYS CHECK
AND VERIFY.
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.
g. Replace orifice with correct size, if required by Table
11. Use only factory- -supplied orifices. See EXAM-
PLE 1.
Table 9 – Altitude Derate Multiplier for U.S.A.
ALTITUDE
PERCENT
FT. (M)
OF DERATE
0–2000
0
(0--- 610)
2001–3000
8–12
(610--- 914)
3001–4000
12–16
(914--- 1219)
4001–5000
16–20
(1219--- 1524)
5001–6000
20–24
1524--- 1829)
6001–7000
24–28
(1829--- 2134)
7001–8000
28–32
(2134--- 2438)
8001–9000
32–36
(2438--- 2743)
9001–10,000
36–40
(2743--- 3048)
EXAMPLE 1: 0–2000 ft. (0- -610 M) altitude
For 22,000 Btuh per burner application use Table 11.
Heating value = 1000 Btuh/cu ft.
Specific gravity = 0.62
Therefore: Orifice No. 43*
Manifold pressure: 3.7- -In. W.C.
* Furnace is shipped with No. 43 orifices. In this example all
main burner orifices are the correct size and do
not need to be changed to obtain proper input rate.
3. Adjust manifold pressure to obtain correct input rate. (See
Fig. 42.)
a. Turn gas valve ON/OFF switch to OFF.
b. Remove manifold pressure tap plug from gas valve.
c. Connect a water column manometer or similar device
to manifold pressure tap.
d. Turn gas valve ON/OFF switch to ON.
e. Manually close blower door switch.
f. Jumper R and W thermostat connections on control to
start furnace. (See Fig. 26.)
DERATE MULTIPLIER
FACTOR*
1.00
0.90
0.86
0.82
0.78
0.74
0.70
0.66
0.62
36
g. Remove regulator seal cap and turn regulator adjusting
screw counterclockwise (out) to decrease input rate of
clockwise (in) to increase input rate.
h. Install regulator seal cap.
i. Leave manometer or similar device connected and pro-
ceed to Step 4.
NOTE: DO NOT set manifold pressure less than 3.2- -In. W.C. or
more than 3.8- -In. W.C. for natural gas at sea level. If manifold
pressure is outside this range, change main burner orifices.
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.
4. Verify natural gas input rate by clocking meter.
NOTE: Gas valve regulator adjustment cap must be in place for
proper input to be clocked.
a. Turn off all other gas appliances and pilots served by the
meter.
b. Run furnace for 3 minutes in heating operation.
c. Measure time (in sec) for gas meter to complete 1 revolu-
tion and note reading. The 2 or 5 cubic feet dial provides
a more accurate measurement of gas flow.
d. Refer to Table 12 for cubic ft. of gas per hr.
e. Multiply gas rate (cu ft./hr) by heating value (Btuh/cu ft.)
to obtain input.
If clocked rate does not match required input from Step 1,
increase manifold pressure to increase input or decrease manifold
pressure to decrease input. Repeat steps b through e until correct
input is achieved. Reinstall regulator seal cap on gas valve.
5. Set temperature rise. The furnace must operate within the
temperature rise ranges specified on the furnace rating
plate. Do not exceed temperature rise range specified on
unit rating plate. Determine the temperature rise as fol-
lows:
NOTE:
Blower access door must be installed when taking
temperature rise reading. Leaving blower access door off will
result in incorrect temperature measurements. When setup switch
SW1- -4 is ON, operation will be near the high end of the rise
range for improved comfort. Furnace must operate within ranges
of temperature rise specified on the furnace rating plate.
Determine air temperature rise as follows:
WARNING
!
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal injury
or death.
Disconnect 115- -v electrical power and install lockout tag
before changing speed tap.
a. Place thermometers in return and supply ducts as close
to furnace as possible. Be sure thermometers do not see
radiant heat from heat exchangers. Radiant heat affects
temperature rise readings. This practice is particularly im-
portant with straight- -run ducts.
b. When thermometer readings stabilize, subtract return- -air
temperature from supply- -air temperature to determine air
temperature rise.
NOTE: If the temperature rise is outside this range, first check:
(1.) Gas input for heating operation.
(2.) Derate for altitude if applicable.
Advertisement
Table of Contents
