So I have 2 Infinity units on 1st and 2nd floor with dual fuel on 1st floor. I am finishing the basement and going to add zoning to the 1st floor unit for the basement. The upstairs is already a zoning system with 2 zones.

With the colder weather, it would be nice to have gas heat upstairs. Could I have the upstairs as a zone on the 1st floor unit when it calls for aux heat? Ie can the relay that asks for aux to come on, just call for a zone? Ideally it would be for first stage of aux and then if needed, the strips could come on as second stage.

The ducting is not difficult because of a garage.

I can always just make the upstairs a zone for the winter and see how I like it, programmed to call for heat 1st with a higher set temp than the upstairs unit. Not as elegant. Extra stat on the wall to program. Don't know if there would be pressure issues if both units were running.

The furnace is a 60k unit and I used to setback the downstairs at night so that it barely runs. I have since upped it at night to help heat the upstairs which is not ideal. I think in the morning, as it gets to temp, it might have a hard time keeping the upstairs warm also. But really, it runs for 15 minutes on high stage to warm the downstairs 3 degrees so I doubt it would be a problem.

In NC, tight house. 60k on the furnace is on the high side for the downstairs.