I am looking at replacing our 16 year old, upstairs, central AC unit.

It is a 3.5 ton Lennox. I believe it is 10 seer and looking at replacing with a 16 seer 3.5 ton unit.

What is not clear to me is if I need to also replace the evaporator coils or not.

This is based on the evaporator coils are working fine. What is not clear to me is if coils and AC unit types have to go together or not. Also if new coils have improved in a manner that affects the seer number.

Also, if I do replace our coils are the Lennox C23-46-1 which is a relatively weird size of W X D X H of 19.75" x 22.75" x 15".

Looking at the coils that go with the AC unit I am looking at there are none that are very close in size. Our coils are inside the house, vertical and right above the furnace.

The suction and liquid lines are the same size as the replacement unit we are looking at so was not looking at replacing. Curious if in most cases people do replace. BTW, our basement is also finished so changing the lines would be a hassle.

Any help very much appreciated!

 

To achieve the 16 SEER you will have to replace the coil. No need to replace the line set, just make sure they are flushed out.