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For satisfactory operation, propane gas pressure must be
10" WC at the furnace manifold with all gas appli ances 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 con tainer 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 vaporiza-
tion, 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
standard com mercial compounds, special pipe dope must
be used. Always use a pipe thread sealant approved for all
gases.
Refer to the this illustration for typical propane gas
installations and piping.
First Stage
Regulator
200 PSIG
Maximum
Propane Gas Installation (Typ.)
CIRCULATING AIR & FILTERS
Duct work - Air Flow
Duct systems and register sizes must be properly
designed for the CFM and external static pressure rat ing
of the furnace. Design the ductwork in accor dance with the
recommended methods of "Air Conditioning Contractors of
America" Manual D.
Install the duct system in accordance with Standards of the
National Board of Fire Underwriters for the Installation of
Air Conditioning, 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 attached to the back of the furnace. For upflow
installations requiring 1800 CFM or more, use either two
side returns or bottom return or a combination of side /
5 to 15 PSIG
(20 PSIG Max.)
Continuous
11" W.C.
Second Stage
Regulator
Figure 21
bottom. Flexible joints may be used for supply and return
con nections to reduce noise transmission. To prevent the
blower from inter fering 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
(external duct static) rating.
Never allow the products of combustion, including carbon
monoxide, to enter the return duct work or circulation air
supply.
Total external static refers to everything external to the
furnace 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 pressure 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
(inclined manometer) to measure the static pressure
of the return duct at the inlet of the furnace. (Negative
Pressure)
2. Measure the static pressure of the supply duct.
(Positive Pressure)
3. The difference between the two numbers is .4" w.c.
Example:
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.
20
WARNING
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