22
2. With the unit operating, time the smallest dial on the
meter for one complete revolution. If this is a 2 cubic
foot dial, divide the seconds by 2; if it is a 1 cubic foot
dial, use the seconds as is. This gives the seconds
per cubic foot of gas being delivered to the unit.
3. INPUT=GAS HTG VALUE x 3600 / SEC. PER CUBIC
FOOT
Example:
Natural gas with a heating value of 1000 BTU
per cubic foot and 34 seconds per cubic foot as determined
by Step 2, then:
Input = 1000 x 3600 / 34 = 106,000 BTU per Hour.
NOTE: BTU content of the gas should be obtained
from the gas supplier. This measured input must
not be greater than shown on the unit rating
plate.
Adjust input rate by varying the adjustment of the gas
pressure regulator on the gas valve. All adjustments
must be made with furnace operating at high fire and at
normal operating temperature. A manometer should be
connected to the gas valve to verify pressure is within
the specified range (see following figures for manometer
connections). Clockwise rotation of the pressure regulator
screw increases pressure and gas flow rate. Turn screw
counterclockwise to decrease pressure and gas flow rate.
After adjustment the furnace temperature rise must be
within the range specified on the unit data plate.
NOTE: Thermal efficiency of the furnace is a
product efficiency rating determined under
continuous operating conditions independent of
any installed system.
Manometer
Manometer
Hose
High Fire Regulator
Adjust
(Under Cap Screw) Regulator
Vent
Gas Flow
O
N
O
FF
white-rodgers (2-Stage) gas control valve
connected to manometer pressure adjustments
Figure 14
To connect manometer to gas valve:
1. Back outlet pressure tap screw (inside inlet pressure
boss) out one turn (counterclockwise, not more than
one turn).
2. Attach a hose and manometer to the outlet pressure
boss of the valve.
To remove manometer from gas valve:
1. Remove manometer hose from outlet pressure boss.
2. Turn outlet pressure tap screw in to seal pressure port
(clockwise, 7 in-lb. minimum).
3. Turn on electrical power and gas supply to the
system.
4. Turn on system power and energize valve.
5. Using a leak detection solution or soap suds, check
for leaks at pressure boss screw. Bubbles forming
indicate a leak. SHUT OFF GAS AND FIX ALL LEAKS
IMMEDIATELY.
CAUTION
To prevent unreliable operation or equipment
damage, the gas manifold pressure must be as
specified on the unit rating plate. Only minor
adjustments should be made by adjusting the
gas valve pressure regulator.
6.
Relight all other appliances turned off in step 1 of gas
input check. Be sure all pilot burners are operating.
Main Burner Flame Check
Flames should be stable, soft and blue (dust may cause
orange tips but they must not be yellow) and extending
directly outward from the burner without curling, floating or
lifting off.
NOx Screen Check
Verify that the alignment of the NOx screens is at 6
o’ clock. In jurisdictions that do not require low NOx
emissions, NOx screens may be removed.
Temperature Rise Check
Check the temperature rise through the unit by placing
thermometers in supply and return air registers as close
to the unit as possible. Thermometers must not be able to
sample temperature directly from the unit heat exchangers,
or false readings could be obtained.
1. All registers must be open; all duct dampers must be
in their final (fully or partially open) position and the
unit operated for 15 minutes before taking readings
2. The temperature rise must be within the range
specified on the rating plate.
NOTE: Air temperature rise is the temperature
difference between supply and return air.
With a properly designed system, the proper amount of
temperature rise will normally be obtained when the unit
is operated at rated input with the recommended blower
speed.
If the correct amount of temperature rise is not obtained, it
may be necessary to change the blower speed. A higher
blower speed will lower the temperature rise. A slower
blower speed will increase the temperature rise.
