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Diagrams A and B and Table 1 show the maximum equivalent length and size of duct pipe that should be used
when installing the CAS system. Using these charts will help ensure that the proper amount of air is drawn
into the structure as needed by the appliance. The defi ned regions shown correspond to the CAS's airfl ow
characteristics when using 4" and 6" diameter sheet metal duct pipe and the included orifi ce ring. Follow the
guidelines below to properly size and setup the CAS.
1. Determine the maximum input fi ring rate of the appliance, or the maximum total fi ring rate of multiple
appliances that will be used.
2. Position the motorized CAS unit according to the guidelines in the Installation section.
3. Determine where the intake air vent hood will be located based on the recommendations in the Installation
section.
4. The CAS is equipped with a High/Low motor speed control switch. When calculating the maximum equivalent
feet, determine which speed is appropriate for the application. (Refer to Diagram A or B or Table 1)
5. Calculate the total equivalent length of duct pipe including elbows and fi ttings needed to connect the CAS
unit to the vent hood. (Refer to Diagram A or B or Table 1)
6. On Diagram A or B, locate the point that corresponds to the fi ring rate along the horizontal axis and the
equivalent length of the duct pipe along the vertical axis, if using for make up air.
7. The point should fall within one of the three regions on the table. Each region corresponds to a duct pipe
diameter of 4", 4" using the orifi ce ring, and 6" respectively.
GENERAL SYSTEM OPERATION
1. The thermostat (wall thermostat, or aquastat) calls for heat and energizes a relay which activates the CAS
unit. After the CAS fan has come up to speed and air fl ow into the CAS inlet is estabished, an internal
air pressure switch closes and completes the circuit to allow the burner to fi re. If the appliance is power
vented, the venter and CAS activate simultaneously. After the CAS and power venter have come up to
speed, a pressure switch in the power venter control also closes and allows the appliance to fi re.
2. After the heating requirement has been satisfi ed, the thermostat circuit will open and deactivate the
burner and CAS unit.
3. For power vented systems with a post purge device, the power venter and CAS operate for a period of
time after the burner has shut off to purge remaining fl ue gases from the vent system.
INSTALLATION SAFETY INSTRUCTIONS
CAUTION: This device must be installed by a qualifi ed installer in accordance with the manufacturer’s
installation instructions.
1. This combustion air system must be installed by a qualifi ed installer. “Qualifi ed Installer” shall mean an
individual who has been properly trained or a licensed installer.
2. Plan the system layout before installation to avoid the possibility of accidental contact with concealed
wiring or plumbing inside walls.
3. Disconnect power supply before making wiring connections to prevent electrical shock and
equipment damage.
SIZING AND SETUP
P/N 46284600 Rev L 09/19
