17
IO-242
5/04
At all altitudes, the manifold pressure must be within 0.3 inches
w.c. of that listed in the Product Data Book applicable to your
model* for the fuel used. At all altitudes and with either fuel, the
air temperature rise must be within the range listed on the furnace
nameplate. Should this appliance be converted to LP, refer to the
instructions included in the factory authorized LP conversion kit
LPT-00
.
H
IGH
A
LTITUDE
D
ERATE
When this furnace is installed at high altitude, the appropriate
High Altitude orifice kit must be applied. The furnace is supplied
with orifices sized for natural gas at altitudes up to 2,000 feet
using a heating value of approximately 1,000 Btu/hr, and should
not normally require change. If for use at altitudes in excess of
2,000 feet, refer to the instructions included in the factory
authorized high altitude kit
(HA-02).
It is important to check and adjust the input rate of the furnace to
prevent an overfiring situation. Overfiring can cause premature
heat exchanger failure. The input is controlled by the supply
pressure, orifice size, manifold pressure and heating (calorific)
value of the gas.
The supply pressure must be measured with this and all other
gas burning appliances in operation. The supply pressure must
be adjusted to the pressure range stated on the series and rating
plate. Applications for altitudes in excess of 2,000 feet usually
require an orifice change. The orifices must be selected using the
table below. The furnace derate is 4% for each 1,000 feet above
sea level. This table is based upon a heating value of approximately
1,000 Btu/ft
3
NAT. GAS
ORIFICE SIZE
0 - 2,000
#43
3,000
#44
4,000
#44
5,000
#45
6,000
#45
7,000
#46
ALTITUDE
The input to the furnace must be checked AFTER reorificing.
For altitudes above 7,000 feet, refer to appropriate section of the
National Fuel Gas Code, ANSI Z223.1. To calculate the input of
the furnace for installations in altitudes over 2,000 - 7,000 feet,
use the following formula:
Corrected Input = Series & Rating Plate Input - (Altitude X .04) X
(Series & Rating Plate Input / 1000)
Example:
Corrected input for a 90,000 Btu/hr. appliance installed at an
altitude of 6,000 ft. utilizing natural gas with a heating value of
1,000 Btu/ft
3
is determined by-
Corrected Input = 90,000 - (6,000 X .04) X (90,000 / 1,000)
Corrected Input = 90,000 - (240 X 90)
Corrected Input = 90,000 - 21,600
Corrected Input = 68,400
Using the orifices sized as shown in the table for 6,000 feet (#45),
a meter time of 52.6 seconds is measured. The actual firing rate
of the furnace is
Input = 1,000 (heating value of the gas) X 3600 (constant) / 52.6
(meter time for 1 ft
3
of gas)
Input = 3,600,000 / 52.6
Input = 68,400 Btu/h
M
ETER
T
IME
I
N
M
INUTES
AND
S
ECONDS
F
OR
N
ORMAL
I
NPUT
R
ATING
OF
F
URNACES
E
QUIPPED
F
OR
U
SE
W
ITH
N
ATURAL
G
AS
A
T
0 - 2,000 F
EET
A
LTITUDE
INPUT
METER
SIZE
HEAT
VALUE
HEAT
VALUE
HEAT
VALUE
HEAT
VALUE
Btu/hr
FT
3
900
1,000
1040
1,100
MIN. SEC.
MIN.SEC
MIN. SEC.
MIN. SEC.
1
1 21
1 30
1 33
1 39
10
13 30
15 00
15 36
16 30
1
0 54
1 00
1 03
1 06
10
9 00
10 10
10 24
11 00
1
0 41
0 45
0 47
0 50
10
6 45
7 30
7 48
8 15
1
0 32
0 36
0 37
0 40
10
5 24
6 00
6 14
6 36
1
0 27
0 30
0 31
0 33
10
4 30
5 00
5 12
5 30
120,000
40,000
60,000
80,000
100,000
In Canada, the series and rating plate input for the furnace apply
to installations up to 2,000 feet (610m) above sea level. Kit
HA-
02
for natural and LP gases is required to convert furnaces from
elevations of 2,000 to 4,500 feet (610m to 1,370m). Canadian
certification applies to the installations of up to 4,500 feet above
sea level. Installations above 4,500 feet are subject to acceptance
by the local authorities having jurisdiction.
Do
not
derate the furnace by adjusting the manifold pressure to a
lower pressure than specified on the furnace rating plate. The
combination of the lower air density and a lower manifold pressure
will prohibit the burner orifice from drawing the proper amount of
air into the burner. This may cause incomplete combustion,
flashback, and possible yellow tipping.
In some areas the gas supplier may artificially derate the gas in
an effort to compensate for the effects of altitude. If the gas is
artificially derated, the appropriate orifice size must be determined
based upon the BTU/ft
3
content of the derated gas and the altitude.
Refer to the National Fuel Gas Code, NFPA 54/ANSI Z223.1, and
information provided by the gas supplier to determine the proper
orifice size.
A different pressure switch may be required at high altitude
regardless of the BTU/ft
3
content of the fuel used. Contact your
distributor for a tabular listing of appropriate altitude ranges and
corresponding manufacturer’s pressure switch kits.
P
ROPANE
G
AS
C
ONVERSION
WARNING
P
OSSIBLE PROPERTY DAMAGE, PERSONAL INJURY OR DEATH MAY OCCUR IF
THE CORRECT CONVERSION KITS ARE NOT INSTALLED.
T
HE APPROPRIATE KITS
MUST BE APPLIED TO INSURE SAFE AND PROPER FURNACE OPERATION.
A
LL
CONVERSIONS MUST BE PERFORMED BY A QUALIFIED INSTALLER OR SERVICE
AGENCY.
This unit is configured for natural gas. The appropriate
manufacturer’s propane gas conversion kit, must be applied for
propane gas installations. Refer to the “Propane Gas and/or High
Altitude Installations” section for details.
