We have relatively new high efficiency gas furnaces that feed into 100 year old ductwork.
In particular, our 2 third floor bedrooms are fed off the same 9" riser that feed the 2nd floor bedrooms underneath it. As a result, there is much less heat reaching the third floor than the 2nd floor.
Even adjusting the dampers at the takeoffs to the bedrooms has only limited effect, since the airflow is just not powerful enough 3 floors up.
So, I am wondering whether someone makes a booster blower that would sit just below the 3rd floor vent grill and would not require ripping up the walls, ceilings, or floors to install.
Note I know they make inline fans that it into the duct itself, but that would seem to require breaking into the wall to access the duct. I want something that would sit right underneath the vent grill.