[walterc]

I have installed multiple zoned systems along with new duct systems and can have the upstairs colder than the downstairs on a 95* day. If your duct is designed right and you have figured out the load requirements you can heat/cool the space you are trying to condition. It can be done with proper design and implementation.

I agree with you- I've seen a few systems do fine this way.

My problem is, I don't know how to make that design work. Yet I rarely ever have to- I always talk them into two systems.