Question... does your overhead unit have a heat strip, or does your heat come from a separate furnace?
If the latter... chances are you simply have your fan set to also come on when your furnace is on. On my thermostat, there is a MODE button for furnace or A/C... and also a FAN switch that can be placed in HIGH, MED, LOW, or AUTO setting. You want your fan to be in AUTO when your furnace is on... and the overhead blower shouldn't run.
2013 VOLTAGE 3200 (EPIC I & II)
2014 Ford F-450 PLATINUM