Using inline booster fans – GreenBuildingAdvisor

I’m in Washington zone 4C and will be able to upgrade my HVAC with Inflation Reduction Act grants after the beginning of 2025.

My current Trane is 3.5 ton, 13 seer, and uses 3/8″ and 5/8″ lines. My air handler is in the conditioned attic. All my ductwork goes down through the stud bays (lined up with floor joists) and I will reuse all the ducting.

The Trane air flow chart shows the CFM around 1300-1400 while the Mitsubishi SVZ-KP30NA / SUZ-KA30NA2 lists 613 – 875. My concern is that the lower CFM of the central ducted, inverter HP might not get enough heated air down to the finished basement, which is about a 21′ drop from the handler to the ceiling ducts. (basement + main + upstairs + attic).

My question is: Would it be reasonable to use an inline booster fan for the ducts that go to the basement? 

(My 3.5 ton is oversized most of the time, until we get down to 30°F, when it shuts off and goes to heat strips.)