There are 2 rooms that suffer from insufficient airflow from air exchanger heating/cooling. At some pt someone installed an in duct booster fan, -- even recent replacement of air exchanger, the installers were baffled by the fan (and felt it would be costly to get to it); best can tell just clanks & solely moves by push of air passing thru-- the duct at the juncture where it was installed is so bound & cemented, would be difficult to get to. Any power to it no longer cks as functioning either. Seeing there are fan boosters used in place of registers
--wondering if they gain. The registers are at the ceiling, however one needs to be within 1-2 ft to feel any air exiting as is. One room is 5-10 degrees less warm during heating likewise less during cooling season.