Filter
Top Products
18
IO-242C 05/05
using a heating value of approximately 1,000 Btu/hr, and should
not normally require change. Most cases will not require a change
at altitudes up to 7,500 feet. For use at altitudes in excess of 4,500
feet, refer to the following table for maximum input rates based on
altitude. Contact your local gas utility for the heating value of the
gas. Refer to National Fuel Gas Code ANSI Z223.1 and the
following section to calculate firing rates.
Maximium Firing Rates At Altitude
Model (Kbtu/hr)
Altitude (ft) 45 70 90 115 140
5,000 39,000 58,500 78,000 97,500 117,000
7,500 35,000 52,500 70,000 87,500 105,000
10,000 34,000 51,000 68,000 77,000 92,400
* Firing rates may be lower than listed in table
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 4,500 feet usually
require an orifice change. Alternately standard de-rate for altitude
from National Fuel Gas Code ANSI Z223.1 of 4% per 1000’ may
be taken. Refer to the most recent version of ASNI Z223.1 for
correct gas orifice. 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 4,500 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 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:
FIRING R ATE
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
METER TIME IN MINUTES AND SECONDS FOR NORMAL INPUT RATING
OF
FURNACES EQUIPPED FOR USE WITH NATURAL GAS
INP UT M ETER
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 4,500 feet (1370m) above sea level. 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.
Some models require a pressure switch change due to the reduced
air density above certain altitudes. Refer to the following table to
determine proper pressure switch settings for your application.
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 appropriate altitude ranges and pressure switch
kits.
Pressure Switch Changes
Furnace input Kbtu/hr Altitude (ft) Switch Setting (inches w.c.)
45 8000' 0.5
5
70 N
R
90* 8000' 0.
6
11
5
N
R
14
0
N
R
* 904BNA does not require a switch change
PROPANE GAS CONVERSION
WARNING
POSSIBLE 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.