GMVC9 GCVC9 Installation Instructions
31
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 following illustration for typical propane gas instal-
lations and piping.
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 Con-
ditioning, 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 bot-
tom return or a combination of side /bottom. Flexible joints
may be used for supply and return connections to reduce noise
transmission. To prevent the blower from interfering with com-
bustion 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 cham-
ber.
CHECKING DUCT STATIC
N
EVER
ALLOW
THE
PRODUCTS
OF
COMBUSTION
,
INCLUDING
CARBON
MONOXIDE
,
TO
ENTER
THE
RETURN
DUCT
WORK
OR
CIRCULATION
AIR
SUPPLY
.
WARNING
Refer to your furnace rating plate for the maximum ESP
(external duct static) rating.
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 external
static pressure. The supply duct pressure must be read be-
tween the furnace and the cooling coil. This reading is usu-
ally 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 (in-
clined 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.
The temperature rise of the furnace must be within the tem-
perature rise range listed on the furnace rating plate.
BOTTOM RETURN AIR OPENING [UPFLOW MODELS]
The bottom return air opening on upflow models utilizes a “lance
and cut” method to remove sheet metal from the duct opening
in the base pan. To remove, simply press out the lanced sections
by hand to expose the metal strips retaining the sheet metal
over the duct opening. Using tin snips, cut the metal strips and
remove the sheet metal covering the duct opening. In the cor-
ners of the opening, cut the sheet metal along the scribe lines to
free the duct flanges. Using the scribe line along the duct flange
as a guide, unfold the duct flanges around the perimeter of the
opening using a pair of seamer pliers or seamer tongs. NOTE:
Airflow area will be reduced by approximately 18% if duct flanges
are not unfolded. This could cause performance issues and noise
issues.