Everett M. Greene wrote:

I've been contemplating methods of obtaining heat from the attic
for heating the house during appropriate times of the year.
One idea I have is to put a ducted fan in the attic to blow
the warm/hot air into the garage as an initial experiment...

Good idea. For more heat, you might replace a south roof with transparent
polycarbonate Dynaglas greenhouse roofing material, which comes in 4'x12'
corrugated sheets and costs about $1/ft^2 and lasts about 20 years.

You'd also want a return air path and one-way dampers to avoid letting
warm air go up into the attic at night. Return air might go up through
a ceiling register with a box above it and some heavy plastic film hanging
over the screened south wall of the box for a damper. With the transparent
roof, the box could also act as a skylight. Supply air could come from
a fan below the ceiling that pulls attic air down through a tall duct,
with light plastic film hanging over the fan outlet.

I'm also thinking that a reversible ventilator would be in order in that
it could double as a way to vent hot air from the garage into the attic
and out through the roof vents during hot weather.

That's easier, since warm air rises. You might block the roof vents and add
gable vents with doors that open in summertime and close in wintertime.

Nick