Fan Min On Time Operating Algorithms

Q: I noticed something about the way the "fan min runtime" operates on my system. I had it (Fan Min On Time) set to 5 minutes, and when the heat never ran in that hour, the system appeared to divide the 5 minutes into 4 chunks (4 x 1:15s per hour) and cycled every 15 minutes. Is this normal or should the fan run continuously for 5 minutes?

A:  The fan algorithms are designed to divide the fan run times instead of engaging the blower in a block operation. If the Fan Min On Time is set for 15 minutes or lower, the fan will operate in four separate quadrants in the hour. If the Fan Min On Time is set for 20 minutes or higher, the fan will run in equal halves in the hour. Of course, when a non-boiler system is operating, the fan will run the entire time (plus Dissipation time) the heating /cooling system is engaged.