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The supply pressure must be measured with this furnace 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 require an orifice change. The orifices
must be selected using the table below. The furnace de-rate is 4% for each 1,000 feet above sea
level. This table is based upon a heating value of approximately 1,000 Btu/ft
ALTITUDE
0 - 2,000
3,000
4,000
5,000
6,000
7,000
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 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 100,000 Btu/hr. appliance installed at an altitude of 6,000 ft. utilizing natural gas
with a heating value of 1,000 Btu/ ft
Corrected Input = 100,000 - (6,000 X .04) X (100,000 / 1,000)
Corrected Input = 100,000 - (240 X 100)
Corrected Input = 100,000 - 24,000
Corrected Input = 76,000
Using the orifices sized as shown in the table for 6,000 feet (#48), a meter time of 48.0 seconds is
measured. The actual firing rate of the furnace is
Input = 1,000 (heating value of the gas) X 3600 (constant) / 48.0 (meter time for 1 ft
Input = 3,600,000 / 48.0
Input = 76,000 Btu/hr
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 L.P. 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 is subject to acceptance by the
local authorities having jurisdiction.
BEFORE ATTEMPTING ANY SERVICE OR ADJUSTMENTS - INSURE THAT THE GAS AND
ELECTRICAL SUPPLIES ARE "OFF".
IO-176
3
is determined by-
WARNING
18
3
.
NAT. GAS ORIFICE SIZE
#45
#47
#47
#47
#48
#48
3
of gas)
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