Tube it right! Prevent overheating due to low or no airflow
When the heater comes with an airflow switch (fixed PDN or adjustable PDA), some minor field work is required to complete the installation. The mechanical airflow switch is mounted inside the control panel of the heater and will activate internally normally open and normally closed contacts upon required minimum pressure. This is one of the safety features added to the heater to prevent overheating due to low or no airflow. The pvc tube and probe/pitot are supplied loose in a pouch attached to the inside of the panel door. The switch has HIGH and LOW ports. If the duct has positive pressure flowing through the heater, the pvc tube should be inserted on the high port. For negative pressure, insert the tube on the low port.
Nema1 control panels come with a hole on top to bring the tube out. Note that control panels with nema12, nema4 or nema4X construction will not have this hole. These panels are built to be sealed to avoid dust, water, snow etc. But a hole must be made on site by the installer ensuring a proper seal after the tube is brought out.
The other end of the tube will have the probe with airflow direction marked on the back. Insert the probe into the duct making sure that the arrow is in the direction of airflow. If cold spots or blank offs are used in the heater to increase velocity, the probe should be installed downstream of the heater.
Verify velocity at minimum 300 FPM to activate the heater. Note that certain modulating heaters will have electronic airflow sensors (EAS) built-in, instead of mechanical airflow switches, which do not require any field work.
KEEP THE AIR FLOWING...