In dealing with multi zone set ups the enemy is always over capacity. The more speeds the system has the better it will handle a multi zone setup because if you have 1 or 2 zones calling the system is better able to match the capacity needed to the call being received. Even better if you go to a variable speed (compressor) model.

These kinds of systems aren't meant to 'only' save you money on the light bill, the are meant to give you the best in comfort. They will save you money too, but that isn't the only reason to buy one.

You have to think: what is comfort worth to you.

If you pair a full variable speed system (compressor of the condenser is full variable speed not just the furnace blower or furnace blower and condenser fan motor) They make a slew of different model units to confuse you.

So getting back to the point if you have a full variable speed system including the compressor the best way to control this kind of system is via communicating thermostat.

Communicating is different in that the system actually talks with the thermostat(s). Communicating is like having a network run via your thermostat wires. This is only one option, in some cases you could hook these systems up the old fashioned way of power signals.

Problem is the power signal way may cut the functionality somewhat. These systems were designed to 'communicate'.

Proprietary zone boards have their place because they were designed for the system you are attempting to design. Me personally I know there are better options available else where. This comes from over 20 years of experience and heavy control knowledge.

Most zone boards operate via the way of sending a 'voltage signal' the communication application is in it's infancy. These things only started trickling out over the past few years.

The non-propriety zone boards that have communication capabilities come at a hefty cost and in many cases will require more than one board, not to mention the cost of multiple communicating thermostats.

There are ways to cut costs and maintain a good communication balance. But that requires astute control knowledge. Something you may have to look for in many different service providers.

Your service provider will play an integral role. Because this is who you will ultimately call on if the system needs servicing.

Mike, the OP said 'high and dry'.

Due to mountainous range magic 8 ball says: NO GAS.

We're in Bend, OR. House will be 4300 ft. 2 story (2nd is just bedrooms - 1k ft up). We have natural gas but we also need summer cooling.. I hadn't considered mini split. The local contractors said they were steering away from them recently. I don't love the look of the in-room units either.

Bend, OR has a winter design temperature of 4 degrees F. I suggest you get 95%+ efficiency gas furnaces. Two stage variable speed models would be nice. You can pair those with 2-stage AC condensers.

I would recommend separate HVAC systems for the upper and lower floors. If the lower floor is 3300 sq. feet then it would be best if that the downstairs system is zoned.

If the house has a basement then that would be my first choice to install both systems. If you are on a slab then a HVAC room centrally located on the first floor would be good. You want all equipment and duct work in conditioned space whenever possible. Variable speed or modulating furnaces use their own proprietary communication system. You have to get the manufacture's thermostat in order to get all the benefits of the equipment.

Finally make sure the HVAC contractor does a load calculation and have him explain it to you. If it doesn't make sense it is probably wrong.

First bid came back proposing separate downstairs (5ton Trane S9V2 with XL18i AC) and upstairs (2ton same units). We do have quite a few west facing windows for the view but I was surprised with the 7-ton total capacity. He said Bend has only a couple months of AC weather and nobody goes nuts with communicating units. Indeed it was $11K to upgrade to them. Hopefully the two stage is quiet enough. The downstairs system had a separate zone for the Master Bedroom so it had zoning but not much of it.

Really the only reason you would want the communicating systems for that climate is better humidity control. But this will depend on how the house is located because I think some areas of Oregon are less humid than others. If the area this home is in has high humid times (30 days or longer) of 80% or higher, better humidity control is necessary. Homes being built today are tight and once that humidity makes it's way indoors it is hard to get out. Causes tons of problems.

A Trane dealer will tell you this because in order to go communicating with a Trane system you would have to go full variable speed (whole system including the compressor)

Where as other manufacturer's have communicating systems that start at 16 SEER 2 speed compressor.

As it were, the devil is in the details.

Then if Bend only has a couple months of AC weather then why is proposing a condenser that is intended for 18 SEER efficiency?

A 5 ton condenser for the first floor seems over sized. It could be the cooling load calculation came out to 4.1 tons and he rounded up to the next larger size which is 5 tons for the XL18i. You should have him explain the load calculation. Ask what was used for the indoor and outdoor design temperatures.

I believe Oregon has lower than average electricity rates. That being the case I don't think spending extra money on a high SEER condenser is the best use of your money. I also think new construction should be able to work with a 4 ton condenser. The money you save could be put towards a communicating system if Trane has a system that makes sense.

Ideally the contractor sits down with you and reviews several possible options. If he is not interested in doing this then continue looking for contractors.

Thanks all. I did ask as much as I could knowing as little as I do about hvac. He said he calculated 115k btu for heating. 22k of it upstairs. I'm missing my notes for cooling load. I was scribbling madly. We do have a ton of West facing windows in the living room and kitchen but 9ft ceilings so no crazy giant A-Frame window walls. It's quite dry here. The XL18i was probably my fault. I asked for a two stage AC but I see that the 17 is also Two Stage. It was just my attempt to get something that ran quieter and cycled less.

Variable speed is just that in supplying more air faster when the demand is higher. You may need these speeds when you are operating in multiple zones unless you want the air to be the same even when certain zones are off. If you are looking to save money then this should work fine for you without multi speed especially if you are looking for a quicker warm up and don't mind a single speed to your home.. Variable is nice to have but unnecessary if you don't mind.. its a comfort / efficiency thing for sure but really nice to have as a option. Chicago HVAC SERVICE