54
9. Check outlet/manifold gas pressure.
10. Repeat steps 8 and 9 if needed.
11. Remove jumper across R and W1 to remove heat call
and allow blower to finish off delay.
12. Disconnect 115 volt power to furnace.
13. Turn gas off at manual gas valve and remove the
manifold pressure tap and replace with outlet/manifold
pressure tap plug.
14. Set dip SW10 to the OFF position.
15. Reconnect all thermostat connections.
16. Turn on the gas supply and check for leaks using an
approved leak detector. Do NOT use a flame of any
kind to check for leaks. Repair any leaks and repeat.
STEP 3: VERIFY THE INPUT RATE
Once the orifices have been selected and the manifold
pressure set, the input rate of the furnace can be deter-
mined by clocking the amount of time it takes for your
meter to make one revolution. Table 15 specifies the num-
ber of cubic feet per hour based on the number of sec-
onds measured for one revolution of the meter (meters
listed are; (a) one cubic meter per revolution and (b) ten
cubic meters per revolution).
Once you have determined the number of cubic feet per
revolution, the input rate of the furnace can then be deter-
mined using the following formula:
Input Rate = ((Gas Rate (ft
3
/ Hour)) x (Altitude-Adjusted
Gas Heating Value (BTU’s/ft
3
))
Note the units which cancel:
Input Rate = (Gas Rate (ft
3
/Hour) x (Altitude-Adjusted Gas
Heating Value (BTU’s/ft
3
))
Example
:
The following information is determined:
1. Altitude-Adjusted Gas Heating Value = 975 BTU/ft
3
(given from gas supplier)
2. Meter used is 1 revolution per ft
3
3. Time per revolution at high fire = 36 seconds (this is
measured by the installer).
4. From Table 15, the formula for Gas Rate is as follows:
Gas Rate (ft
3
/hr) w 1ft
3
/Rev Meter = (3600)/(Revolu-
tion Time (in seconds))
Gas Rate (ft
3
/hr) w 1ft
3
/Rev Meter = (3600)/(36 Sec-
onds)
Gas Rate = 100 ft
3
/Hour
(Note this value could have also been taken directly
from Table 15).
Input Rate = ((Gas Rate (ft
3
/ Hour)) x (Altitude-Adjusted
Gas Heating Value (BTU’s/ft
3
))
Fill in the values:
Input Rate = ((100ft
3
/Hour) x (975 BTU’s/ft
3
)
Input Rate = 97,500 BTU’s/Hour
If the rate calculated does not match the furnace input on
the rating label (below 2,000 ft) or the elevation-corrected
rate calculated in item of above (
Selecting the Orifices
)
(at or above 2,000 ft in elevation) /-5%, the next
larger orifice (if rate is too low) or the next smaller orifice (if
the rate is too high) must be installed and the process re-
peated from (Adjusting the Gas Pressures).
Repeat steps 2 and 3 until the proper rate is achieved
with the manifold pressure within the tolerances spec-
ified herein.
When both of these adjustments are correct,
proceed to Step 4,
Adjusting Gas Heat Temperature
Rise
.
To determine the gas flow rate, calculate the cubic ft per
hour use the following formulas or use the following table:
Gas Rate (ft
3
/hr) w 1ft
3
/Rev Meter = (3600)/(Revolution
Time (in seconds))
Gas Rate (ft
3
/hr) w 2ft
3
/Rev Meter = (7200)/(Revolution
Time (in seconds))
Gas Rate (ft
3
/hr) w 5ft
3
/Rev Meter = (18000)/(Revolution
Time (in seconds))
FURNACE ADJUSTMENTS
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