75
SETTING GAS PRESSURE
The maximum gas supply pressure to the furnace
must not exceed 10.5" w.c. natural gas, or 13" w.c. LP
gas. The minimum supply gas pressure to the gas valve
should be 5⬙ w.c. natural gas or 11⬙ w.c. LP gas. A properly
calibrated manometer is required for accurate gas pres-
sure measurements.
SUPPLY GAS PRESSURE
MEASUREMENT
A line pressure tap is on the input side of the gas valve.
1. With gas shut off to the furnace at the manual gas
valve outside the unit, remove the input pressure tap
plug.
2. Connect a manometer to the pressure tap.
3. Turn on the gas supply and operate the furnace and all
other gas-fired units on the same gas line as the fur-
nace.
4. Note or adjust the line gas pressure to give:
A. 5⬙ - 10.5⬙ w.c. for natural gas.
B. 11⬙ - 13⬙ w.c. for LP gas.
5. Shut off the gas at the manual gas valve and remove
the manometer.
6. Replace the pressure tap plug before turning on the
gas.
If the supply gas line pressure is above these ranges, in-
stall an in-line gas regulator to the furnace for natural gas
units. With LP gas, have the LP supplier reduce the line
pressure at the regulator.
If supply gas line pressure is below these ranges, either re-
move any restrictions in the gas supply piping or enlarge
the gas pipe. See Tables 3 and 4. With LP gas, have the
LP supplier adjust the line pressure at the regulator.
Manifold Gas Pressure Measurement. Natural gas
manifold pressure should be 3.5" w.c. LP gas manifold
pressure should be 10.0" w.c. Only small variations in
gas pressure should be made by adjusting the pressure
regulator.
1. With the gas to the unit shut off at the manual gas
valve, remove the outlet pressure tap plug.
2. Connect a manometer to this pressure tap.
3. Turn on the gas supply and operate the furnace.
4. Note or adjust the manifold gas pressure to give:
A. 3.5⬙ w.c. for natural gas.
B. 10.0⬙ w.c. for LP gas.
5. To adjust the pressure regulator, remove the regulator
cap.
6. Turn the adjustment screw clockwise to increase pres-
sure, or counterclockwise to decrease pressure.
7. Securely replace the regulator cap.
8. Shut off gas at the manual gas valve and remove the
manometer.
9. Replace the pressure tap plug before turning on the
gas.
GAS PRESSURE
GAS PRESSURE
Gas Pressure
!
CAUTION
ELEVATIONS ABOVE 2000 FT. REQUIRE THAT THE
FURNACE INPUT RATING BE ADJUSTED AND THAT
THE SIZE OF THE BURNER ORIFICES BE RECAL-
CULATED BASED ON ELEVATION AND GAS HEAT-
ING VALUE. THE BURNER ORIFICES MAY (OR MAY
NOT) NEED TO BE CHANGED. SEE THE SECTION
TITLED “HIGH ALTITUDE INSTALLATIONS” OF THIS
BOOK FOR INSTRUCTIONS.
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