DUAL FUEL with 80 or 90%

[2story]

In a dual fuel setup HP with gas backup, I would tend to think that a 80% furnace would be the best route to offset the high cost of the HP. which do you recommend and why, my climate is so. indiana.

[docholiday]

Well if you have any cooling load, you can be rest assured that your SEER will lose about a point when on a 90 versus an 80 because of the secondayr HX. And that can also affect the HSPF. If it were me, an 80+ with VS would be ideal.