The AHRI data for Carrier/Bryant shows 3 and 4 ton coils with the same furnace and condenser will produce the same EER and SEER ratings. I have never understood why. You would think a bigger coil would improve the efficiency.

I had a similar choice when I purchased by Carrier equipment. I chose to get the biggest coil the with a valid AHRI match. The issue is the 3 ton coil is 17 inches wide while the 4 ton is 21 inches. It is not a big problem. A transition duct can be made to put a 21 inch coil on a 17 inch furnace. This is what I have on one of my furnaces.

My suggestion would be to get the bigger coil assuming it will not cause an installation problem when you get a new furnace. The SEER rating will likely be the same or very close with either coil.

Thank you Mike.

I just did some more reading and my understanding is that the bigger the coil, the better the efficiency but less dehumidifying effect. So for a more humid area, it is suggested not to over sizing the coil.

I have also read a bigger coil means a less dehumidifying effect. However I based on my personal experience I can great humidity control with my over sized coils and Carrier Infinity furnace and AC.

I think an over sized coil may have more of an effect on the humidity control on fixed speed equipment versus variable speed. The most important thing is to properly size the condenser.