START-UP PROCEDURE AND ADJUSTMENT
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 installations requiring more than 1800 CFM, use a bottom return or two sided return. Supply and return connections to the furnace may be made with flexible joints to reduce noise transmission. To prevent the blower from interfering with combustion air or draft when a cen- tral return is used, a connecting duct must be installed be- tween the unit and the utility room wall. A room, closet, or alcove must not be used as a return air chamber.
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 condensation in the heating element. With a parallel flow arrangement, 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.
When the furnace is installed without a cooling coil, it is rec- ommended that a removable access panel be provided in the outlet air duct. This opening shall be accessible when the fur- nace is installed and shall be of such a size that the heat exchanger can be viewed for visual light inspection or such that a sampling probe can be inserted into the airstream. The ac- cess panel must be made to prevent air leaks when the furnace is in operation.
When the furnace is heating, the temperature of the return air entering the furnace must be between 55°F and 100°F.
When a furnace is installed so that supply ducts carry air cir- culated by the furnace to areas outside the space containing the furnace, the return air shall also be handled by a duct sealed to the furnace casing and terminating outside the space con- taining the furnace.
CHECKING DUCT STATIC
Refer to your furnace rating plate for the maximum ESP (exter- nal 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 pres- sure. The supply duct pressure must be read between the fur- nace 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.
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 =
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, regis- ters, undersized and/or oversized poorly laid out duct work.
Checking Static Pressure
(80% Furnace Shown, 90% Similar)
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.
FILTERS - READ THIS SECTION BEFORE INSTALLING THE RETURN AIR DUCTWORK
Filters must be used with this furnace. Discuss filter mainte- nance with the building owner. Filters do not ship with this furnace, but must be provided by the installer. Filters must com-
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