420705-UIM-C-0310
24
Johnson Controls Unitary Products
CALCULATING THE FURNACE INPUT
(NATURAL GAS)
Burner orifices are sized to provide proper input rate using natural gas
with a heating value of 1030 BTU/Ft
3
(38.4 MJ/m
3
). If the heating value
of your gas is significantly different, it may be necessary to replace the
orifices.
Verify natural gas input rate by clocking meter.
1.
Turn off all other gas appliances and pilots.
2.
Run furnace for a minimum of 3 minutes in heating operation.
3.
Measure time (in sec) for gas meter to complete 1 revolution and
note reading. The 2 cubic feet dial provides a more accurate mea-
surement of gas flow.
4.
Refer to Table 14 for cubic feet of gas per hour.
5.
Multiply cubic feet per hour by heating valve (BTU/cu ft) to obtain
input.
If clocked rate does not match the input rate from the unit nameplate.
follow steps in next section to adjust the manifold pressure. Repeat
steps 2 - 5 until correct input is achieved.
HOT SURFACE IGNITION SYSTEM
Do not attempt to light this furnace by hand (with a match or
any other means). There may be a potential shock hazard from
the components of the hot surface ignition system. The fur-
nace can only be lit automatically by its hot surface ignition
system.
DO NOT set manifold pressure less than 3.2” w.c. or more than 3.8”
w.c. for natural gas at sea level. If manifold pressure is outside this
range, change main burner orifices.
If orifice hole appears damaged or it is suspected to have been
redrilled, check orifice hole with a numbered drill bit of correct size.
Never redrill an orifice. A burr-free and squarely aligned orifice hole
is essential for proper flame characteristics.
NOTICE
NOTICE
DO NOT bottom out gas valve regulator adjusting screw. This can
result in unregulated manifold pressure and result in excess over-
fire and heat exchanger failures.
Be sure to relight any gas appliances that were turned off at the
start of this input check.