UL BADF090 Installation Instruction
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Contents
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ADJUSTMENT OF TEMPERATURE RISEThe temperature rise (or temperature difference between thereturn air and the heated air from the furnace) must lie withinthe range shown on the U.L. or CGA rating plate and the datain Table 2.After the temperature rise has been determined, the cfm canbe calculated as follows:After about 20 minutes of operation, determine the furnacetemperature rise. Take readings of both the return air and theheated air in the ducts (about six feet from the furnace) wherethey will not be affected by radiant heat. Increase the blowercfm to decrease the temperature rise; decrease the blower cfmto increase the rise. Refer to Table 8 for blower motor and drivedata.BELT DRIVE BLOWERAll units have belt drive single-speed blower motors. Thevariable pitch pulley on the blower motor can be adjusted toobtain the desired supply air CFM.CHECKING GAS INPUTNATURAL GAS1. Turn off all other gas appliances connected to the gas meter.2. With the furnace turned on, measure the time needed forone revolution of the hand on the smallest dial on the meter.A typical gas meter usually has a 1/2 or a 1 cubic foot testdial.3. Using the number of seconds for each revolution and thesize of the test dial increment, find the cubic feet of gasconsumed per hour from Table 11.If the actual input is not within 5% of the furnace rating (withallowance being made for the permissible range of theregulator setting), replace the orifice spuds with spuds of theproper size.NOTE To find the Btu input, multiply the number of cubic feet ofgas consumed per hour by the Btu content of the gas inyour particular locality (contact your gas company for thisinformation - it varies widely from city to city.)CFM = Btuh Input x 0.81.08 x oF Temp. RiseSecondsfor OneRev.Size of Test Dial1/2 cu. ft. 1 cu. ft.1012141618180150129113100360300257225200202224262890827569641801641501381293032343638605653504712011310610095404244464845434139379086827875505254565860363534323130726967646260Example: By actual measurement, it takes 19 seconds for the hand on the 1-cubicfoot dial to make a revolution with just a 100,000 Btuh furnace running. Using thisinformation, interpolate for 19 seconds in the first column in the table above. Readacross to the column headed “1 Cubic Foot”, where you will see that 190 cubicfeet of gas per hour are consumed by the furnace at that rate. Multiply 190 x 1050(the Btu rating of the gas obtained from the local gas company). The result is199,500 Btuh, which is close to the 204,000 Btuh rating of the furnace.TABLE 11 - GAS RATE - CUBIC FEET PER HOURSECURE OWNER’S APPROVAL:When the system is functioning properly, secure the owner’s approval. Show himthe location of all disconnect switches and the thermostat. Teach him how to start and stop the unit and how to adjust tem-perature settings witnin the limitations of the system.511.17-N2W16 Unitary Products Group |
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