Here at Firestat, we sell our duct limit control switches to a few larger companies. Today, we thought we would highlight one. The company we are looking at today is our distributor, Dynacon. Dynacon is an HVAC distributor located in Virginia. They sell our Firestat switches to construction companies who are building or maintaining apartment buildings. Our high limit switches are approved for use in high density residential buildings in North Carolina to shut off fans in case of a fire. This prevents smoke from being blown through the ductwork into the rest of the building. Not only will this prevent smoke from moving to the rest of the building, but it can help stop the spread of the fire as well. It is why some US states, like North Carolina, require duct limit control switches in buildings to meet their Mechanical Building Code.

If you’re interested in becoming a distributor like Dynacon, contact us!

Duct Building CodeNow you may be wondering, what is a building code? “A building code, or building control, is a set of rules that specify the minimum standards for constructed objects such as buildings and non-building structures. The main purpose of building codes is to protect public health, safety and general welfare as they relate to the construction and occupancy of buildings and structures. The building code becomes law of a particular jurisdiction when formally enacted by the appropriate governmental or private authority.” – Wikipedia

Many local and regional building codes require the use of a sensing device to shut-down the airflow in the event of a critical temperature increase in the air ducts. This code was applied to mainly multi-family dwellings that shared a common HVAC system. The theory was to contain the smoke and prevent it from spreading to multiple units.


Many buildings decided to have an exhaust fan installed within their duct space to maintain cool temperatures inside the building. Once the air temperature reaches a pre-determined set point, a fan switch powers on an exhaust fan to keep the building from overheating.

If a fire is present within the system, the fan will feed the flames and the building will be up in smoke quickly. By installing a duct high limit switch, this risk can be reduced. The high limit switch is installed within the exhaust system, and when higher air temperature is reached due to fire the limit switch will shut the exhaust fan down preventing the spread.

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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.