Choosing the correct bimetal length for duct limit switches is actually quite easy but very important. Choosing the wrong probe length can cause your switch to not function properly when neededYou should always be sure to determine your Limit Switch Element Length prior to purchasing. 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. To make it simple, the larger the air duct, the longer the element required. If too short of an element length the duct limit switch may receive inaccurate temperature readings causing the switch to trigger at too low of a temperature, or delay. Click here to purchase our Firestat Duct Limit Switches!

Choosing the Correct Bimetal Length

You’ve decided to purchase a Firestat to keep your home or your building safe, great choice! Now you’re looking at your options and see there are 3 different probe length, but you’re wondering, what’s the difference? Our adjustable temperature range Firestats come in probe lengths of 5-inch, 7.5inch and 11inch. Choosing the correct length for your duct will allow the Firestat to work properly when you need it to. In order to determine which length you will need, you’ll have to know the approximate size of the duct it will be installed in. The end of the probe that sits inside the duct should sit closest to the dead center of the duct as possible. This allows the Firestat to properly read the air temperature effectively, without getting a misread from the temperature on the sides of the duct.

Tips to Remember

  1. Make sure to measure the size of your duct before purchasing a Firestat.
  2. Choosing the correct probe length will allow your Firestat to work properly when it needs to.
  3. Probe length needed will be determined by how large the duct it’s being installed in is.
  4. Choose the probe length that will allow it to sit as close to the dead center of the duct as possible.

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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.