duct heater

[direwolf]

Hello, I have a question that has been puzzling me. I have been given the task to figure out how to make a duct heater blower fan run after the thermostat has stopped calling. What I have is a 480V 3phase unit that is working off of a 24V transformer to feed my thermostat and my airflow sensor, which then goes to my 2 contacts. What I want to do is after the blower fan kicks off, the airflow sensor stops sensing air, and the coil turns off I want the blower fan to keep running for a minute or two. I can't seem to figure out how to get around the air flow sensor. If the sensor is closing then the coil will come on. I want to get the residule heat out of the duct basically. Anyone have any ideas. thanks

[mikejacobson]

I recently had this issue but a little different. What is starting the fan on a call for * the stat or some type of fan relay in * In some cases I've had to upgrade thermostat and change set up to electric heat mode, which keeps fan on for short time after satisfied. You also could use a fan time delay relay (solid state) that is used for a little better seer rating on a/c units when furnaces were old school.