Field controls CAS-4 User Manual

COMBUSTION AIR SYSTEM

Model: CAS-4

ITEMS INCLUDED IN KIT:

1) Motorized Blower

1) 4" galvanized intake air Vent Hood

2) Mounting brackets to secure the CAS to a wall

2) Wire/conduit connector(s)

1) 4" x 6" Pipe Increaser Fitting

1) 6" Orifice Ring

1) Instruction Sheet

1) High/Low Motor Speed Switch

This product is designed for use with any natural gas or LP burning furnace,
water heater, or boiler with a 24 VAC control system. It may be used with a
millivolt powered system with additional hardware. It may also be used with
more than one appliance. The CAS unit mechanically draws air into a
structure and disperses it near the combustion air intake of an appliance. If an
optional Vacuum Relief Valve (VRV) is used, the incoming air is tempered
before entering the structure's airspace. Refer to Diagram A and B for
guidance in setting up the CAS system based on the size and length of the
connecting duct-work and the input rating of the appliance.

This device MUST be installed by a qualified agency in accordance with the manufacturers installation
instructions.

The definition of a qualified agency is: any individual, firm, corporation or company which either in person or through a
representative is engaged in, and is responsible for, the installation and operation of gas appliances, who is experienced
in such work, familiar with all the precautions required, and has complied with the requirements of the authority having
jurisdiction.

DO NOT DESTROY

THESE INSTRUCTIONS MUST REMAIN WITH EQUIPMENT

2630 Airport Road · Kinston, NC 28504

2630 Airport Road · Kinston, NC 28504

Phone: [phone]· Fax: [phone]

Phone: [phone]· Fax: [phone]

www.fieldcontrols.com

www.fieldcontrols.com

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, an internal air pressure switch closes and
completes the circuit to allow the burner to fire. If the appliance is power vented, the venter and
CAS activate simultaneously. After the CAS comes up to speed, a pressure switch in the unit
closes and allows the appliance to fire.

2. After the heating requirement has been satisfied, 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 flue gases from the vent system.

INSTALLATION SAFETY INSTRUCTIONS
CAUTION: This device must be installed by a qualified installer in accordance with the manufacturer's

installation instructions.

1. This combustion air system must be installed by a qualified installer. "Qualified 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

Diagrams A and B and Table 1 shows 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 defined regions shown
correspond to the CAS's airflow characteristics when using 4" and 6" diameter sheet metal duct pipe
and the included orifice ring. Follow the guidelines below to properly size and setup the CAS.

1. Determine the maximum input firing rate of the appliance, or the maximum total firing 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 t he
"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 fittings 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 firing 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 orifice ring, and 6" respectively. If the point falls near the
rightward border of a particular region then the VRV is not necessary. If the point falls away from
the rightward border, then a VRV is needed to reduce the amount of air drawn in.

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8. Draw a horizontal line on Diagram A or B that passes through the point located in step 5. The
position of the point along this line relative to the left and right borders of the region it falls into
indicates the relative position that the balance weight of the VRV should be adjusted to. If the
point falls near the leftward border of a region, then the VRV balance weight should be adjusted to
it's minimum position. This corresponds to turning the balance weight screw as far counter­clockwise as possible.

EXAMPLE: A gas fired appliance firing at 100,000 BTU/hr where the CAS unit needs to be placed 30
equivalent feet from the intake hood.

From Diagram A or B, the point at 100,000 BTU/Hr on the "Gas Firing Rate" scale
and 30 equivalent feet falls in the "4 inch Duct, Hood, and Orifice Ring" region.
The point is approximately 2/3 of the horizontal distance between the left and right
boundary of the region. The left boundary is the edge of the graph, the right
boundary is the diagonal line that says "4 inch Duct, Hood & Orifice Ring."
Therefore, place the Orifice Ring into the inlet of the CAS so that it sits on the
ledge above the fan. It does not matter which way the Orifice Ring is turned as
long as it is pushed down against the ledge completely. Use 4" diameter pipe to
connect the vent hood and the CAS unit. Install a VRV and the included 4x6 inch
Increaser on top of the CAS unit and adjust the balance weight to 2/3 of the
distance of it’s full adjustment range from it’s minimum setting. The minimum
setting is with the balance weight turned all of the way counterclockwise.

Table 1

Total Input of

Appliance

CAS-4,4mV

Gas

(BTU/hr)

50,000 300 300 300 300 300 300

75,000 300 300 300 300 300 300
100,000 300 300 300 300 300 300
125,000 300 220 300 220 300 300
150,000 174 108 232 118 300 300
175,000 99 48 152 63 300 300
200,000 52 14 102 32 300 300
225,000 20 NA 68 13 300 239
250,000 NA NA 45 NA 300 150
300,000 NA NA 16 NA 300 53
350,000 NA NA NA NA 193 8
400,000 NA NA NA NA 109 NA
450,000 NA NA NA NA 56 NA

4” Duct And Hood

W/Restrictor

HI LOW HI LOW HI LOW

Maximum Equivalent Feet of Installation

4” Duct And 4”

Intake Air Hood

6” Duct And 6”

Intake Air Hood

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HIGH SPEED SIZING CHART

A

OIL INPUT FIRING RATE (gallons per hour)

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

300

250

200

150

100

MAX. EQUIVALENT DUCT LENGTH (ft.)

50

0

0 50 100 150 200 250 300 350 400 450 500 550

(1 gallon oil/hr = 140,000 BTU/hr)

6" Duct & Hood
4" Duct & Hood
4" Duct, Hood, & Orifice

GAS INPUT FIRING RATE (1000 BTU/hr.)

Diagram

LOW SPEED SIZING CHART

OIL INPUT FIRING RATE (gallons per hour)

0.00 0.50 1.00 1.50 2.00 2.50

300

250

200

150

100

MAX. EQUIVALENT DUCT LENGTH (ft.)

50

0

0 50 100 150 200 250 300 350 400

(1 gallon oil/hr = 140,000 BTU/hr.)

6" Duct & Hood
4" Duct & Hood
4" Duct & Hood w/ Orifice

GAS INPUT FIRING RATE (1000 BTU/hr.)

Diagram B

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