14
Check both manifold pressure (using the 1/8" NPT tap located on the gas valve) and service pressure (using the 1/8" NPT
tap as shown in the drawing above).
GAS PIPE CAPACITY TABLE (CU. FT./HR)
Capacity of gas pipe of different diameters and length in cu. ft. per hr. with pressure drop of 0.3 in. and specific gravity of
0.60 (natural gas). NOTE : COPPER TUBING MUST NOT BE USED FOR NATURAL GAS INSTALLATIONS.
Nominal Iron Length of Pipe, Feet
Pipe Size, Inches 10 20 30 40 50 60 70 80
1/2 132 92 73 63 56 50 46 43
3/4 278 190 152 130 115 105 96 90
1 520 350 285 245 215 195 180 170
1 1/4 1050 730 590 500 440 400 370 350
1 1/2 1600 1100 890 760 670 610 560 530
After the length of pipe has been determined, select the pipe size which will provide the minimum cubic feet per hour required
for the gas input rating of the furnace using the formula :
Cu. Ft.Per Hr. Required = Gas Input of Furnace(BTU/HR)
Heating Value of Gas (BTU/HR)
The gas input of the furnace is marked on the furnace rating plate. The heating calorific value of the gas (BTU/Ft
3
) may be
determined by consulting the local natural gas utility or the L.P. gas supplier.
If your local utility/ building codes permit the use of a flexible gas line ALWAYS USE A NEW LINE. DO NOT USE FLEXIBLE
GAS LINES WHICH HAVE PREVIOUSLY SERVICED ANOTHER APPLIANCE.
CIRCULATING SUPPLY AIR AND RETURN AIR.
The circulating air return may be taken from:
(1) outside the building (2) return ducts from several rooms (3) central return (4) any combination of the above.
Note: When outside air is utilized, the system should be designed and adjusted such that the temperature of the air supply
to the furnace will not drop to below 50°F during the heating season.
When a combination of indoor and outside air is used (in conjunction with a mixing or diverting damper) the volume of air
must not be reduced.
Plenum chambers and air ducts must be installed in accordance with Standard for the Installation of Air Conditioning and
Ventilating Systems, NFPA No. 90A, or the Standard for the Installation of Warm Air Heating and Air Conditioning Systems,
NFPA No. 90B.
When the ducts are installed so that the supply ducts carry air circulated by the furnace to area outside the space containing
the furnace, the return air shall be handled by a duct or ducts sealed to the furnace casing and terminated outside the space
containing the furnace. If there is no complete return air duct system, the return air connection must be sealed to the furnace
casing and run full size to a location outside the utility room or space housing the furnace. The furnace must be installed
in a level and plumb position.
If installed in parallel with a cooling unit, the damper or other means used to control the flow of air must be adequate to prevent
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