Description

Adjustable Temperature Duct Limit Controls (Firestat)

The Firestat Adjustable Temperature Duct Limit Switch is a UL Recognized manual-reset safety control designed to protect commercial HVAC systems from overheating. Adjustable from 100°F to 250°F, it automatically opens the control circuit when duct temperatures exceed the selected setpoint, helping protect equipment and supporting fire safety requirements in air handling systems, electric duct heaters, and multi-family buildings.

Each Firestat control incorporates a precision helix bi-metal sensing element that delivers accurate temperature sensing and long-term reliability. As duct temperature rises, the bi-metal element expands and actuates a snap-action SPST switch, opening the electrical circuit to safely shut down the heating equipment. Once the unsafe temperature condition has been identified and corrected, the control must be manually reset before the HVAC system can resume operation. This manual reset feature helps ensure the root cause of the over-temperature event is addressed before the equipment is placed back into service.

Manufactured by Senasys, Firestat duct limit controls are built for dependable performance in demanding HVAC applications. Every switch is 100% functionally tested before leaving our manufacturing facility to ensure consistent quality, accuracy, and reliable operation in the field.

Key Features

• • Adjustable temperature range from 100°F–250°F
  • Manual reset for added safety
  • Available with 5″, 7.5″, or 11″ sensing probes
  • Helix bi-metal sensing element
  • Opens on temperature rise (SPST)
  • UL Recognized
  • Manufactured in Wisconsin, USA
  • Individually tested before shipment
  • Compatible with commercial HVAC and electric duct heaters
  • OEM customization available

Typical Applications

Firestat Adjustable Duct Limit Controls are commonly installed in:

• • Commercial HVAC systems
  • Apartment and condominium HVAC systems
  • Schools, hospitals, and institutional buildings
  • Industrial Systems

How It Works

As air temperature inside the duct increases, the sensing element continuously monitors the airflow temperature. When the selected temperature setpoint is reached, the switch opens to interrupt power to the heating equipment or control circuit. The control remains open until the manual reset button is pressed, providing an added layer of safety by requiring the overheating condition to be investigated before restarting the system.

Installation Instructions

Built for HVAC Safety

Firestat Duct Limit Controls are engineered for dependable performance in demanding HVAC environments. Whether you’re replacing an existing duct high limit control or specifying a safety device for new equipment, Firestat delivers the quality and reliability trusted by HVAC contractors, OEMs, and facility managers.

Product Specifications

View Datasheet

Adjustable vs. Fixed Duct High Limit Controls

Frequently Asked Questions

Here’s a list of commonly asked questions. Visit our FAQ page for more information.

• How do I adjust the temperature?
  • It’s simple. Remove the cover and adjust the dial. Learn more here.
• What is the factory default setting?
  • Our adjustable duct high limit controls ship factory set at 125°F.
• Which probe length should I choose?
  • Probe length is dependent on the size of the air duct. Learn more here.
• Can I order custom probe lengths?
  • Yes, please contact our technical support with more information.
• Is this UL Recognized?
  • Yes.
• Can this replace a Honeywell L4029E?
  • Yes. Visit our cross reference table for more information.
• Can it replace a Johnson Controls A25AN-1?
  • Yes. Visit our cross reference table for more information.
• Does it require manual reset after activation?
  • Yes. Learn more about how these controls work here.

Need Assistance?

Not sure which temperature range or sensing element length is right for your application? Our technical support team can help you select the appropriate Senasys Duct Limit Control for your HVAC system or OEM design. Custom options available, such as, temperature ranges, element lengths & fixed temperatures. Click here to Contact us to discuss your requirements.

Need more than 20 units?

Request OEM pricing, custom temperature settings, or engineering assistance. Most quote requests receive a response within one business day.

Prefer to work through a distributor?

Firestat duct high limit controls are trusted by contractors, manufacturers, distributors and maintenance teams across North America. If you prefer working with a distributor, visit one of our partner websites here.