That re-cycled heat is only going to be a small fraction of the heat coming down the duct.
The solar heat 'storage' in my attic is very stratified.
This is caused by solar warmed air flowing upwards and accumulating in the peak.
While the attic
floor air temp is sometimes actually
colder than it is outdoors.
Because, the attic's thermal mass tends to hold on to that nighttime temp,
and in the morning, it's in the shade, like the north side of the house.
So, if you had outdoor heat sensors and in the peak that would trigger the fan, when it was needed..
A. Mini-Split running in heating mode.
B. Attic air temp a few deg F warmer than outdoor air.
It might even be useful during those early morning Defrost cycles..
