My fireplace has two blowers behind grates in the brick. Fans behind these lower grates mix air with heated air from behind the firebox and kick out a serious amount of heat into the room. The heated air is forced out of the upper grates on each side of the fireplace.
I have created a golf simulator in my garage and am looking at heating options. Is having a mason create another tunnel/branch terminating in the garage, though the cinder block possible? The garage is located immediately behind the fireplace.