Duct limit control devices are engineered to shut down HVAC equipment when duct air temperatures exceed safe thresholds. These controls play a defined role in fire prevention by interrupting fans, dampers, or other duct-connected components using mechanical thermal sensing. In HVAC systems subject to strict code compliance, including jurisdictions in California, North Carolina, Louisiana, and New York, duct limit control solutions such as Firestat provide a manual reset mechanism and dependable temperature activation.
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Mechanical Function of Duct Limit Control in HVAC Systems
Firestat duct limit control units incorporate bi-metal sensing elements that mechanically react to rising duct air temperatures. Once a defined setpoint between 100°F and 250°F is exceeded, the switch opens the circuit to deactivate equipment such as fans or motorized dampers.
This immediate shutdown prevents air movement through the duct network, helping isolate heat or smoke in the event of fire. External mounting allows for simplified reset access and ensures the sensing element does not obstruct airflow within the duct.
Manual Reset Enhances HVAC Safety Protocols
Duct limit control units from Firestat include a manual reset mechanism that keeps HVAC systems offline after activation until a technician manually resets the switch. This feature aligns with building codes that require positive intervention before systems resume operation after a fault or temperature event.
Applications in multifamily housing or classroom ventilation systems benefit from this approach by providing a layer of safety control that cannot be overridden by automatic system reboots.
Meets Key Mechanical Building Code Requirements
Firestat duct limit control products are certified to meet multiple state-level mechanical code standards:
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North Carolina: Complies with Mechanical Code 607.3.1 requiring fan shutdown upon over-temperature detection
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Louisiana: Aligns with Code 717.3 requiring manual reset for limit controls in heat-producing HVAC systems
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California: Listed under CSFM State Fire Marshal #3225-0981:103
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New York City: Approved under MEA #260-91-M for mechanical shutdown devices
This broad compliance supports HVAC integration across residential, commercial, and institutional projects where safety codes mandate thermal shutdown of duct systems.
Firestat Duct Limit Control Technical Specifications
Firestat products are engineered to support high-performance HVAC control with the following technical specifications:
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Temperature Range: Fixed or adjustable from 100°F to 250°F
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Probe Sizes: Available in 5”, 7.5”, or 11” lengths
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Operating Conditions: Enclosure rated from -40°F to 190°F, with sensing element tolerating up to 350°F
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Installation: External mounting for ducts; accessible manual reset
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Customization: Private labeling and OEM options available for volume deployments
These parameters allow for flexible deployment in both low-CFM duct systems and larger HVAC installations requiring precise thermal shutoff.
Common Use Cases in Code-Driven HVAC Installations
Duct limit control devices are widely used in systems where targeted shutdown is required to meet code or enhance safety:
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Multifamily Housing: Prevents upward or cross-unit fire spread through shared return ducts
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Schools and Institutions: Integrates with rooftop units and ducted classroom systems to enforce thermal safety shutdowns
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Commercial HVAC Systems: Supports code-compliant shutoff in air handlers and fan systems, particularly in heat pump applications under 2,000 CFM
Manual reset control and accurate temperature trip points allow Firestat switches to serve as core components in fire protection strategies.
Duct limit control devices deliver precise and code-compliant HVAC shutdown functionality. Firestat products offer a bi-metal sensing response, a wide thermal range, and manual reset capability to support mechanical building code compliance across multiple regions.
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