a local propane gas supplier about installing a gas detecting
warning system. If the presence of gas is suspected, follow
the instructions listed in the Safety Considerations section
of this manual.
All propane gas equipment must conform to the safety
standards of the National Board of Fire Underwriters, NBFU
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
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 stan-
dard 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 instal-
lations and piping.
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
5 to 15 PSIG
(20 PSIG Max.)
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 /
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.
EVER ALLOW THE PRODUCTS OF COMBUSTION
TO ENTER THE RETURN DUCT WORK OR CIRCULATION AIR
Total external static refers to everything external to the
furnace cabinet. Cooling coils, filters, ducts, grilles, regis-
ters must all be considered when reading your total exter-
nal 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
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
2. Measure the static pressure of the supply duct. (Positive
3. The difference between the two numbers is .4" w.c.
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.