48
Table 12 – Altitude Derate Multiplier for U.S.A.
ALTITUDE --- FT (M)
PERCENT OF DERATE
DERATE MULTIPLIER FACTOR*
0–2000(0---610)
0
1.00
2001–3000 (610---914)
4---6
0.95
3001–4000 (914---1219)
6---8
0.93
4001–5000 (1219---1524)
8---10
0.91
5001–6000 1524---1829)
10---12
0.89
6001–7000 (1829---2134)
12---14
0.87
7001–8000 (2134---2438)
14---16
0.85
8001–9000 (2438---2743)
16---18
0.83
9001–10,000 (2743---3048)
18---20
0.81
* Derate multiplier factors are based on midpoint altitude for altitude range.
h. Jumper R to W/W1.
i. Let furnace run for 3 minutes in low--heat operation.
j. Measure time (in sec) for gas meter to complete 1 re-
volution. Note reading.
k. Refer to Table +13 for cubic ft of gas per hr.
l. Multiply gas rate cu ft/hr by heating value (Btu/cu ft).
m. Move setup switch SW1--2 to OFF position and jumper
R and W/W1 and W2 thermostat connections. (See Fig.
33.) This keeps furnace locked in high--heat operation.
Repeat items i through l for high--heat operation.
UNIT DAMAGE HAZARD
Failure to follow this caution may result in component
damage due to flame impingement of burners and heat
exchangers.
DO NOT redrill orifices. Improper drilling (burrs,
out--of--round holes, etc.) can cause excessive burner noise
and misdirection of burner flames. (See Fig. 52.)
CAUTION
!
EXAMPLE:
(High--heat operation at 0 -- 2000 ft. (610 M)
altitude)
Furnace input from rating plate is 100,000 Btuh
Btuh heating input = Btuh/cu ft X cu ft/hr
Heating value of gas = 975 Btuh/cu ft
Time for 1 revolution of 2--cu ft dial = 70 sec
Gas rate = 103 cu ft/hr (from Table 13)
Btuh 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.
NOTE
: Measured gas inputs (high heat and low heat) must be
within
±
2 percent of that stated on furnace rating plate when
installed at sea level or derated per that stated above when installed
at higher altitudes.
n. Remove jumper across R, W/W1, and W2 thermostat
connections to terminate call for heat.
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 unit
rating plate. Operation is within a few degrees of midpoint
of rise range when setup switch SW1--4 is OFF.
CAUTION
!
Furnace must operate within ranges of temperature rise specified
on the furnace rating plate. Determine air temperature rise as
follows:
1. Place thermometers in return and supply ducts as near fur-
nace as possible. Be sure thermometers do not see heat ex-
changer 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
temperature from supply--air temperature to determine air
temperature rise.
NOTE
:
Temperature rise can be determined for low--heat
operation by placing setup switch SW1--2 on furnace control in
ON position. For high--heat operation, place setup switch SW1--2
in OFF position and jumper R--W2 on furnace control. DO NOT
forget to return setup switch to OFF position and remove R--W2
jumper upon completion of testing. (See Fig. 33 for switch and
terminal location.)
3. This furnace is capable of automatically providing proper
airflow to maintain the temperature rise within the range
specified on furnace rating plate. If temperature rise is out-
side this range, proceed as follows:
a. Check gas input for low-- and high--heat operation.
b. Check derate for altitude if applicable.
c. Check all return and supply ducts for excessive restric-
tions causing static pressure greater than 0.5--in. wc.
d. Ensure Low Heat Rise Adjust switch SW1--3 on furnace
control is in ON position when a bypass humidifier is
used. (See Fig. 33 for switch location.)
e. Check Troubleshooting Guide for Variable--Speed
2--Stage Electronic Condensing Furnaces Series 100.
355B
A
V
