You have questions. wE have answers.
How does a firestat duct limit switch work?

These Firestat duct fan and limit switches are installed in air ducts to shut down heating, air conditioning and ventilation equipment when air temperature exceeds a pre-set limit.

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How do I install a limit switch?

It’s simple!

  1. Set the temperature dial.
  2. Mount the switch downstream of air flow.
  3. Wire the switch to your equipment.

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What should be my temperature set point?

The temperature you’ll need your Firestat to be set at depends on how close you place it to your furnace and how hot your furnace runs. We recommend that you identify where you plan on installing your duct limit switch before you buy it and measure the air temperature when your furnace is running. Once you know that temperature, add about 40°F and that’s what you should set your switch at.

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What element length should I choose?

When mounting a duct limit switch, it’s best if the bi-metal element reaches the middle of the air duct. The air in the middle of the duct is often a different temperature than the air towards the edge of the duct due to change in pressure and turbulence. When air turns or encounters resistance the air flow speed and temperature are affected. 

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How do I adjust the temperature set point?
  1. Remove the cover
  2. Adjust the dial to the desired set point
  3. Replace the cover & Install

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What’s the difference between a limit and fan switch?

A limit switch shuts down a piece of equipment versus a fan switch turns equipment on. Click here to learn more!

Why is the switch a manual reset vs. an automatic reset?

To ensure the potential fire does not spread to the rest of the building. 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.

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Why bi-metal?

The way Bimetal works is that two different types of metal are fused together. The two metals have different coefficients of thermal expansion, which basically means that they expand at different rates when they heat up. In the case of our switches, the bimetal is in a coil, and the expansion and contraction of the coil is what causes the switch to trigger and open the contacts.

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I have a Honeywell, or Johnson Controls, limit switch. Will your’s work?

Our duct limit switches can be a direct replacement option to your Honeywell or Johnson Controls model. Click here to reference your part number to ours!

Where is the CEMCO firestat line manufactured?

CEMCO Firestat duct limit switches are manufactured in the U.S.A.

Do you sell your products globally?

CEMCO firestat duct limit switches can be found worldwide. We can ship directly to you, or you can work with one of our distributors. Click here to contact us today!

I’m a distributor, can I sell your products?

CEMCO’s firestat duct limit switch is commonly found with HVAC distributors, and we offer wholesale pricing!  Click here to contact us today!

I’m a contractor, can I buy direct?

CEMCO’s firestat duct limit switch is commonly found in large dwellings as a building code requirement. Purchase directly from us for faster lead times and best possible price! Click here to contact us today!

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