SYSTEM OPERATION
18
WARNING
To avoid possible unsatisfactory operation
of equipment damage due to underfiring or
equipment, use the proper size of natural/
propane gas piping needed when running pipe
from the meter/tank to the furnace.
Checking Duct Static
WARNING
Never allow the products of combustion,
including carbon monoxide, to enter the return
duct work or circulation air supply.
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,
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:
-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
temperature rise range listed on the furnace rating plate.
Digital
Manometer
Checking Static Pressure
When the furnace is used in connection with a cooling unit,
the furnace should be installed in parallel with or on the
upstream side of the cooling unit to avoid condensa tion
in the heating element. With a parallel flow arrange ment,
the dampers or other means used to control the flow of
air must be adequate to prevent chilled air from entering
the furnace and, if manually operated, must be equipped
with means to prevent operation of either unit unless the
damper is in the full heat or cool position.
WARNING
Edges of sheet metal holes may be sharp. Use
gloves as a precaution when removing sheet
metal from return air openings.
