4 Yrs old Concord- CG80UB125D20C up-flow furnace remain, replace 26 yrs AC split with York LX Series YCJF36 split - AC coil model FC36.
Will the Concord up-flow air furnace be adequate for this new 3 ton split system proposed for 1800 living space?

4 Yrs old Concord- CG80UB125D20C up-flow furnace remain, replace 26 yrs AC split with York LX Series YCJF36 split - AC coil model FC36.
Will the Concord up-flow air furnace be adequate for this new 3 ton split system proposed for 1800 living space?

It should
You will need to change the evaporater coil if you are going from a r-22 refrigerant to r410A refrigerant,and the lineset

Not real sure if that furnace will move 1200 cfm might be close.

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In the old days the correct airflow was not nearly as critical as it is in today's new higher efficiency A/C's