The Cas 3, along with other models like the CAS 4, are crucial components in ensuring safe and efficient combustion in various appliances. These systems, often referred to as “Fan-in-a-Can,” provide a vital source of combustion air, especially in confined spaces where direct air supply to the burner is limited. This article delves into the functionality and applications of the CAS 3 system.
CAS 3: Ensuring Proper Combustion Air Supply
According to industry standards like NFPA 54 and NFPA 31, adequate combustion air is essential for safe and efficient appliance operation. When appliances are situated in confined areas, ensuring sufficient air intake can be challenging. This is where engineered systems like the CAS 3, CAS 4, and other similar models come into play. They overcome the limitations of restricted spaces by actively supplying the necessary combustion air.
The CAS 3 and CAS 4 (now unified as the CAS 34U) are specifically designed for situations where a direct connection for air intake to the burner isn’t feasible. These systems guarantee a consistent flow of outside air to the burner area, promoting complete and efficient combustion.
Variations and Applications of the CAS System
Different models cater to specific appliance types and BTU requirements. The CAS-4MV, for instance, is tailored for 750mV power pile gas appliances. Each variant incorporates safety mechanisms, including a proving device that prevents burner ignition without a functioning Fan-in-a-Can system. For installations involving multiple appliances, employing multiple CAS units or supplementary controls is necessary.
A smaller version, the Fan in a Can Jr. (CAS-4Jr.), is designed for gas appliances with up to 110,000 BTU/hr input. This model includes a 4″ intake Air Hood (IAH) and mounting brackets for wall installation. It’s commonly used with residential water heaters, often requiring the addition of a control kit like the CK-20 FV/FG for optimal performance.
How the CAS 3 and CAS 4 Operate
The operation of the CAS 3 and CAS 4 follows a straightforward sequence:
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Initiation: When the thermostat (or aquastat) signals a heating demand, a relay activates the CAS unit. The fan within the CAS starts, and once it reaches operational speed, an internal pressure switch closes, completing the circuit and allowing the burner to ignite. In power-vented appliances, the venter and CAS activate concurrently.
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Shutdown: When the thermostat no longer detects a heating need, the circuit opens, deactivating both the burner and the CAS unit.
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Post-Purge (Power Vented Systems): Systems equipped with a post-purge function will continue to operate the power venter and CAS for a short period after burner shutdown. This action effectively removes residual flue gases from the venting system.
Conclusion: The Importance of CAS 3 in Combustion Safety
The CAS 3 and similar systems play a crucial role in ensuring safe and efficient combustion in various applications. By providing a reliable source of combustion air, especially in confined spaces, these systems contribute significantly to the proper functioning of appliances while adhering to safety standards. Understanding the role and operation of the CAS 3 is essential for anyone involved in the installation or maintenance of gas appliances.
