Location please.

What size are systems you are considering replacing?

What zoning controls has dealer quoted?

Post back.

IMO

the system that is failing is a Lennox HP26-018-10p. He was recommending keeping the two thermostats where they are currently located for he individual systems. The other I am considering replacing is a Lennox 12hpb30-2p

Your location please?

What zoning controls have been proposed for the 4 ton system?

IMO

I am in Eastern NC. I don't see any notes on what types of zoning controls were proposed.

You should find out what zoning controls are being proposed and what ductwork modifications will be required to go to one system with two zones controlled by zoning controls.

The downside? Generally you will get better comfort and control with two separate systems. And then if the system goes down, all the living area will be without conditioned air rather than just part of the upstairs.

IMO

Thanks for the help. I'll find out what controls are to be used, he did say no changes to ductwork, it is in good condition and can be tied right into new handler/controls.

I would spend the extra money and replace the two units. You should get a discount by doing both at the same time. You could also do one at a time if the funds are not available.

For Tiger93

Anyone considering using zoning controls should do their due diligence and verify dealer's competence and experience in this area.

I am not against the idea. You just want to verify dealer knows what he's doing. I suggest getting some references with telephone numbers who you can call and find out their experience. Perhaps even visit.

IMO

The zone control would be Honeywell HZ 432 for the XL16i or the HZ 321 for the XR15.

Now you need to confirm dealer's qualifications with zoning controls and ductwork changes.

IMO