Getting quotes for my 2,900 sq feet split level house. I just put a 650 sq feet addition on over the garage. The outside is 3.5 tons and air handler in attic is 5 tons. I thought I wanted two units - one for the upstairs and force the existing unit to cool the downstairs.
One contractor said that adding zoning costs more than I can ever recoup in energy savings.
Another contractor said that the Carrier Infinity is the best at zoning and it would be possible without costing too much more.
I have read through many posts but I have not found one that gave me a simple overview of zoning with one system and how it uses dampers and a variable speed air handler.
Here are the facts: I want two zones - one for upstairs and one for the small "middle level" and downstairs of the split-level home. I guess that when I open the upstairs thermostat, the damper electronically closes the duct(s) that feeds the entire downstairs (typically, is there one duct or multiple ducts that feed downstairs?). If I open the downstairs thermostat, the damper closes the duct(s) that feeds the entire upstairs. Obviously, when both thermostats are opened, the dampers open up and the full 5 ton unit is blasting throughout the whole house.
Let me know if I'm wrong on that understanding. That brings me to my next question - how does a 5 ton unit uses less tonnage when only one zone is being called for (to avoid short-cycling)? Does the variable speed air handler come into play? Meaning, if only one zone is used, the variable speed air handler would go on low speed (hopefully enough the cool the one level). Obviously, if both zones are used, the air handler goes on high speed (no speed in between?).
That brings me to my last question. If I have a central return installed in the upstairs hallway (currently on the slanted ceiling above the staircase), can that be used in a two-zone system? That is, if I just want to cool the downstairs, the one central return will pull the hot/humid air from the downstairs to the upstairs hallway? Or does another return have to be installed?
I thought this would be a good post to cover some of the basics that other newbies might not be aware of. Your thoughts would be much appreciated on this.