g. Look through sight glass in burner enclosure and check
burner flame. Burner flame should be clear blue, almost
transparent. (See Fig. 59.)
h. Remove jumper from R and W.
3. Verify natural gas input rate by clocking gas meter.
NOTE: Be sure all pressure tubing, combustion-air and vent
pipes, and burner box cover front are in place when checking input
by clocking gas meter.
a. Calculate high-altitude adjustment (if required).
UNITED STATES
At altitudes above 2000 ft, this furnace has been approved
for a 2 percent derate for each 1000 ft above sea level. See
Table 11 for derate multiplier factor.
CANADA
At installation altitudes between 2001 to 4500 ft, this
furnace must be derated 5 percent by an authorized Gas
Conversion Station or Dealer. To determine correct input
rate for altitude, see example above and use 0.95 as derate
multiplier factor.
b. Reinstall burner box cover.
c. Gas valve regulator seal cap MUST be on.
d. Turn off all other gas applications and pilots.
e. Start furnace and let operate for 3 minutes.
f. Measure time (in sec) for gas meter to dial to complete 1
revolution.
g. Refer to Table 12 for cu ft of gas per hr.
h. Multiply gas rate (cu ft/hr) X heating value (Btu/cu ft)
using natural gas heating value from local gas
utility/supplier.
EXAMPLE: (0-2000 ft altitude)
Furnace input from rating plate is 100,000 Btuh.
Btu heating input = Btu/cu ft X cu ft/hr
Heating value of gas = 975 Btu/cu ft
Time for 1 revolution of 2-cu ft dial = 70 sec
Gas rate = 103 cu ft/hr (from Table 12)
Btu heating input = 103 X 975 = 100,425 Btuh.
In this example, the orifice size and manifold
pressure adjustment is within ±2 percent of the
furnace input rate.
SET TEMPERATURE RISE
UNIT DAMAGE HAZARD
Failure to follow this caution may result in overheating the
heat exchangers or condensing flue gases in heat exchanger
areas not designed for condensate.
Temperature rise must be within limits specified on furnace
rating plate. Recommended operation is at midpoint of rise
range or slightly above.
Determine and adjust air temperature rise as follows:
1. Place 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 readings. This
practice is particularly important with straight-run ducts.
2. When thermometer readings stabilize, subtract return-air tem-
perature from supply-air temperature to determine air tem-
perature rise.
3. Adjust temperature rise by adjusting blower speed. Increase
blower speed to reduce temperature rise. Decrease blower
speed to increase temperature rise.
Fig. 58—Orifice Holes
A93059
BURNER
ORIFICE
EXAMPLE:
100,000 Btuh input furnace installed at 4300 ft.
Derate Furnace Input Rate
Furnace Input Rate X Multiplier = at Installation
at Sea Level Factor Altitude
100,000 X 0.91 = 91,000
Table 11–Altitude Derate Multipler for U.S.A.
ALTITUDE
(FT)
PERCENT
OF DERATE
DERATE MULTIPLIER
FACTOR*
0–2000 0 1.00
2001–3000 4–6 0.95
3001–4000 6–8 0.93
4001–5000 8–10 0.91
5001–6000 10–12 0.89
6001–7000 12–14 0.87
7001–8000 14–16 0.85
8001–9000 16–18 0.83
9001–10,000 18–20 0.81
* Derate multiplier factors are based on midpoint altitude for altitude range.
Fig. 59—Burner Flame
A89020
BURNER FLAME
BURNER
MANIFOLD
48
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