GCSS96 Installation Manual
30
For satisfactory operation, propane gas pressure must be 10”
WC at the furnace manifold with all gas appliances in operation.
Maintaining proper gas pressure depends on three main factors:
1. Vaporization rate, depending on temperature of the
liquid, and “wetted surface” area of the container or
containers.
2. Proper pressure regulation. (Two-stage regulation is
recommended for both cost and efficiency).
3. Pressure drop in lines between regulators, and between
second stage regulator and the appliance. Pipe size
will depend on length of pipe run and total load of all
appliances.
Complete information regarding tank sizing for vaporization,
recommended regulator settings, and pipe sizing is available
from most regulator manufacturers and propane gas suppliers.
Since propane gas will quickly dissolve white lead and most stan-
dard commercial compounds, special pipe dope must be used.
Always use a pipe thread sealant approved for all gases.
Refer to the illustration for typical propane gas installations and
piping.
N
EVER
ALLOW
THE
PRODUCTS
OF
COMBUSTION
,
INCLUDING
CARBON
MONOXIDE
,
TO
ENTER
THE
RETURN
DUCT
WORK
OR
CIRCULATION
AIR
SUPPLY
.
WARNING
C
IRCULATING
A
IR
& F
ILTERS
DUCT WORK - AIR FLOW
Duct systems and register sizes must be properly designed for
the CFM and external static pressure rating of the furnace. De-
sign the ductwork in accordance with the recommended meth-
ods of “Air Conditioning Contractors of America” Manual D.
Install the duct system in accordance with Standards of the Na-
tional Board of Fire Underwriters for the Installation of Air Condi-
tioning, Warm Air Heating and Ventilating Systems. Pamphlets
No. 90A and 90B.
A closed return duct system must be used, with the return duct
connected to the furnace. NOTE: Ductwork must never be at-
tached to the back of the furnace. For upflow installations re-
quiring 1800 CFM or more, use either two side returns or bottom
return or a combination of side /bottom. Flexible joints may be
used for supply and return connections to reduce noise transmis-
sion. To prevent the blower from interfering with combustion air
or draft when a central return is used, a connecting duct must be
installed between the unit and the utility room wall. Never use a
room, closet, or alcove as a return air chamber.
CHECKING DUCT STATIC
Refer to your furnace rating plate for the maximum ESP (ex-
ternal duct static) rating.
Total external static refers to everything external to the fur-
nace cabinet. Cooling coils, filters, ducts, grilles, registers
must all be considered when reading your total external static
pressure. The supply duct pressure must be read between
the furnace and the cooling coil. This reading is usually taken
by removing the “A” shaped block off plate from the end on
the coil; drilling a test hole in it and reinstalling the block off
plate. Take a duct static reading at the test hole. Tape up
the test hole after your test is complete. The negative pres-
sure must be read between the filter and the furnace blower.
Too much external static pressure will result in insufficient
air that can cause excessive temperature rise. This can cause
limit switch tripping and heat exchanger failure.
To determine total external duct static pressure, proceed as
follows;
1. With clean filters in the furnace, use a draft gauge (in-
clined manometer) to measure the static pressure of the
return duct at the inlet of the furnace. (Negative Pres-
sure)
2. Measure the static pressure of the supply duct. (Positive
Pressure)
3. The difference between the two numbers is .4” w.c.
Example:
-1
0
1 2
3
Difference is 4
static reading from return duct = -.1" w.c.
static reading from supply duct = .3" w.c.
total external static pressure on this system = .4" w.c.
NOTE: Both readings may be taken simultaneously and read
directly on the manometer if so desired. If an air conditioner
coil or Electronic Air Cleaner is used in conjunction with the
furnace, the readings must also include theses components,
as shown in the following drawing.
4. Consult proper tables for the quantity of air.
If the total external static pressure exceeds the maximum
listed on the furnace rating plate, check for closed dampers,
registers, undersized and/or oversized poorly laid out duct
work.
The temperature rise of the furnace must be within the tem-
perature rise range listed on the furnace rating plate.