Single 5 ton vs 2 3 tons with Gas furnace?

[moby1]

I have an 11 year old two story house that has a single 5 ton Carrier that had a butchered installation that wouldn't pass code today. The system provides the proverbial hot up year around! I have had contractors speak about zoning systems versus installing 2 seperate units. Besides the obvious of more expense for two units to maintain and slightly higher total cost...I would appreciate any feedback.

Units I'm considering are Ruud, Amana & Trane (14/15/16 seer?). Thoughts?

What is the significance of re-using the copper freon line changing from R22 to 410a?

Extended warranties --worth their while?

Better or worst zoning systems with digital programming?

[beenthere]

2 syystems gives you a redundency if one unit breaks on a weekend, you have the other unit to fall back on till a tech can come out.
A zoned system can provide the same comfort as 2 systems. Sometimes better then 2 systems.

Oversizing is even more problamatic with 2 systems then with one. Even though your second floor wasn't cooling right, I would be concerned increasing to 2-3 tons units from a single 5 ton.
Most of the time, its a duct issue causing your type of problem, not the size of the unit.
Get another estimate, from a company that will do a load calc on your home.

[troyorr]

What are the code violations of your existing system? Did one of your bid contractors tell you there were code violations with the existing system? Sounds like a complete tearout and replacement is warrented. The construction and layout of your house will determine if single zoned system or two systems would work best. Have the bidders do Manual J for loads and then Manual D for duct system layouts. Tell them you want two run. One for zone, one for two system. We have installed both ways and customers are happy. Your lifestyle and home design will influence/determine the type of system you get.

[dash]

Zoning is the wy to go,IMHO.

Why have double the components to maintain and eventually replace?

[Daltex]

Zoning is the wy to go,IMHO.

Why have double the components to maintain and eventually replace?

Isn't the negative against zoning the complexity of the design/install? If you find a great contractor then zoning if possible? I'd definetly not only ask for references but possibly even visit a prior install on a AC day and check temp. balance. Does this seem reasonable?

[beenthere]

So people may not like other people snooping through their house checking temps.

[Daltex]

So people may not like other people snooping through their house checking temps.

That would be be kind of a funny request.