Duct High Limit SwitchDuct high temperature limit switches are designed to sense rapid increases in duct temperature, such as those caused by fire. When that high temperature is sensed, the SPST switch inside the Firestat triggers furnace/fans in the duct to shut off, to ensure the potential fire does not spread to the rest of the building. Once the danger has passed, the manual switch ensures that human interaction is needed in order to reset that switch to allow the furnace/fans to turn back on. If an automatic switch was used and switched the furnace/fans back on too soon, it could cause the potential fire to be spread throughout the building. Therefore, a manual switch is the safest route for your duct high limit switch to ensure a potential fire does not spread through your building. Purchase a Duct High Limit Switch by Clicking Here!

Duct High Limit Switch

Now that you know why a manual is better than an automatic, you’ll need to know how to reset your Firestat switch. First, there is the manual reset button. This button is inside of all our Firestat switches that reactivates the temperature limit after the high-temperature condition has cleared. Our switches use a bimetal coil to open a set of contacts when they heat up. However, you may be wondering what these contacts look like, and how they are reset after the switch has been triggered. When placed in an HVAC duct system, it will sense the air temperature. Based on what temperature the device is set at, it will open the contacts whenever that temp is reached, and stop the fan from running and spreading the potential fire or smoke it detected to other areas of the building.

Once the contacts are opened, the switch needs to be manually reset. However, the switch can only be reset once the temperature of the bimetal goes below whatever the switch is set to. This manual reset button reactivates the temperature limit after the high-temperature condition has cleared. It is a manual reset as to make sure someone has to physically check the area to make sure the danger has cleared before the device can be reset back to normal. This prevents any further damage from happening if it were an auto reset and did not require human intervention.

Once the switch cools down, it is reset with the level on the top of the switch, as seen below. You simply pick up on the metal flap and let it “snap” back down, resetting the switch inside the device.

That’s all there is to it! Firestat switches are easy to install and use.


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CEMCO Duct Limit Switches

The Firestat Duct Fan and Limit Thermostat Switches operate using the same physics to ensure HVAC safety. A helix bi-metal element senses a rapid temperature change. When the temperature changes the bi-metal expands and triggers a snap action switch and either opens or closes a circuit. These switches are commonly installed in air ducts designed to shut down heating, air conditioning and ventilation equipment in apartment complexes and other multiple dwelling units when air temperature exceeds the set point.

UL & cUL Approved
Made in the U.S.A.