I have a 2 story house, 4000 sq. ft, that has two furnaces in the basement.
The first floor heats and cools okay.
The second floors, 2/3's of the upstairs nearest to the furnace gets sufficient airflow and heats and cools like you would expect a 2nd floor (less efficient than first floor due to heat loss in the ducts, but still acceptable).
There is one very isolated branch which runs to the remaining 1/3'rd of the upstairs which is the master bedroom and bath. This of course gets no airflow as it's the furthest branch from the furnace. There's almost nothing coming out of the supply lines.
I've checked all inline dampers on the 2nd floor system and played with balancing, and I think the furnace fan is just straight up too weak to run the system out to this last 1/3'rd of the house.
There's no other magic levers I can come up with too pull, and I've disassembled the HVAC duct run up until the point it goes up exterior walls. There's cold air as far as I can follow the duct, but once it has to go up two stories there just isn't enough push.
In the master bedroom, I've kind of just accepted to run a portable AC / electric heater for the seasons and just move on. But, I'm wondering if a 260 CFM booster fan could help on the main duct which supplies this last 1/3rd?
There's a really good point (I'm in Chicago, everything is piped in... electric box is real close) about 20' from the 2nd furnace into this lone run that supplies that upstairs area where I could put in a booster fan.
Has anyone ever installed one of these rectangular duct fans and thinks you could get a meaningful boost on a main branch? There's probably 3 or 4 supply runs that are another 35' (7" to 4" off this branch which run to the master bedroom and bath), and if this could help boost them maybe it'd be worth trying (but if it would require 4 boost fans on each supply [which the manual seems to allude too], I don't see the economic value versus the spot heating / cooling and getting a bigger furnace blower when the current one dies).
Anyone ever driven a few supply lines off of a blower like this with positive results?
[Overall, cheap builder house -- no optimization whatsoever HVAC wise. I'm sure the HVAC contractor was not paid to crank out 100 houses in this subdivision and calculate anything].