507651-01
Issue 1907
Page 27 of 32
Supply Pressure Measurement
A threaded plug on the inlet side of the gas valve provides
access to the supply pressure tap. Remove the threaded
plug, install a field provided barbed fitting and connect
a manometer to measure supply pressure. See Table 9
for proper line pressure. Replace the threaded plug after
measurements have been taken.
On multiple unit installations, each unit should be checked
separately, with and without units operating. Supply
pressure must fall within range listed in Table 9.
Manifold Pressure Measurement
To correctly measure manifold pressure, follow the steps
below:
1. Remove the threaded plug from the outlet side of the
gas valve and install a field-provided barbed fitting.
Connect measuring device “+” connection to barbed
fitting to measure manifold pressure.
2. Start unit and allow 5 minutes for unit to reach steady
state.
3. After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in
4. Shut unit off and remove manometer as soon as an
accurate reading has been obtained. Take care to
remove barbed fitting and replace threaded plug.
5. Start unit and perform leak check. Seal leaks if found.
For safety, connect a shut-off valve between the
manometer and the gas tap to permit shut off of gas
pressure to the manometer.
IMPORTANT
Unit
Fuel
Manifold Pressure
Line Pressure
All
Nat
3.2 - 3.6
4.5 - 10.5
Table 9. Supply Line and Manifold Pressure
(inches w.c.)
Proper Combustion
Furnace should operate a minimum 15 minutes with correct
manifold pressure and gas flow rate before checking
combustion. Take combustion sample beyond the flue
out let and compare to Table 10. The maximum carbon
monoxide reading should not exceed 100 ppm.
Table 10.
Unit
CO
2
% for Nat
All
6.5 - 7.5
High Altitude
Units are NOT approved for installations over 4500 ft.
