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GS110 DIRECT VENT BOILER INSTALLATION AND OPERATION INSTRUCTIONS Page 25
Figure 20- Air and Manifold Pressure
BOILER CHECKING & ADJUSTMENT
INPUT RATE
Gas appliances are rated based on sea level operation
with no adjustment required at elevations up to 2000
feet. At elevations above 2000 feet, input ratings should
be reduced by 4% for each 1000 feet above sea level.
Check the input rate as follows:
NATURAL GAS:
1. Turn off all other gas appliances that use the same
gas meter as the boiler.
2. Call the gas company for the gas heating value.
3. Start the boiler and let it run for 15 minutes.
4. Using the gas meter and a stopwatch, clock the time
that it takes to burn 10 cubic feet of gas and divide
the time by 10.
5. Insert the heating value and the time, in seconds,
into the formula below.
Input Rate = Heating Value(Btu/ft
3
)(3600 s/hr)
Flow Rate(s/ft
3
)
EXAMPLE: If the heating value = 1000 Btu/ft
3
and the flow rate = 36 s/ft
3
Input Rate = (1000 Btu/ft
3
)(3600 s/hr)
36 s/ft
3
Input Rate = 100,000 Btu/hr
If the computed rate deviates by more than 5% from the
rated input value of the unit adjust the gas valve
pressure accordingly. DO NOT adjust the manifold
pressure by more than 5%. If a proper rate cannot be
maintained without adjusting the manifold pressure
beyond the 5% limit, the burner orifice must be replaced.
If the input rate is too low go to the next larger size
orifice. if the input rate is too high, go to the next smaller
size orifice.
PROPANE GAS:
The input rate for LP units is factory set based on the
orifice size. The manifold pressure must be set at 1.9"
W.C. and the orifice supplied with the boiler used unless
the unit is to be derated for altitude.
CAUTION: Never increase the input to the boiler
above that for which it is rated. Doing so can cause
premature failure of the boiler!
GAS PRESSURE ADJUSTMENT
NATURAL GAS:
Optimum results are obtained when the boiler is
operated at its full input rating, with 1.9" W.C. of manifold
pressure. The manifold pressure should not be more that
5% off this value. The gas valve pressure regulator has
been preset at the factory. If adjustment is necessary
the following steps must be followed:
1. Connect each side of a manometer to the two
pressure ports shown in Figure 20 to obtain the
manifold pressure.
2. Connect a flue gas analyzer to the vent pipe.
3. Rotate the regulator adjustment screw clockwise to
increase the manifold pressure, counterclockwise to
decrease it. Never force the regulator adjustment
screw or the gas valve will be damaged!
4. The CO
2
reading should fall between 7% and 9%
with a CO reading of less than 50 ppm air free.
5. Adjust the air damper using the screw on the front
of the filter box if the CO
2
and CO readings are not
within the range given in step 4.
6. Recheck the manifold pressure and adjust it if
necessary.
7. Replace the regulator adjustment screw cap and
pressure port caps once the boiler is properly set
up.
PROPANE GAS:
A manifold pressure of 1.9" W.C. must be maintained
for proper operation of the boiler. If the manifold
pressure is off by more than 5% or if the CO2 and CO
readings are not within the range specified in step 4
above, adjust it according to steps 1 through 7 above.