Switching to Two Zone Heating - http://www.hvacmechanic.com/ Forums
Original message
| Bunbun000001
 |  "Switching to Two Zone Heating"
, posted Tue 25 Oct 09:40  
We have a 2,400 sq foot, four bedroom colonial with natural gas forced air central air conditioning and heating . The problem is that it's all on one zone with the thermostat in the living room on the first floor. In the winter the downstairs is warm the upstairs is freezing and in the summer the downstairs is cool and the upstairs is hot. We are thinking of putting in a second zone for the upstairs and was just wondering what that entailed. Is it a big job? Do we need a second furnace? Do we need another AC unit outside? We live just outside NYC and was wondering what a job like this can cost. Any information would be great.
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| Freon
| "Re(1):Switching to Two Zone Heating" , posted Tue 25 Oct 14:21
The constraint you have to work within if you stay with the one furnace/AC system is air flow. The AC evaporator coil and furnace heat exchanger must have a certain amount of air flow to function efficiently and safely. So closing off vents alone won't usually help because you're lessening the air flow. You'll need to add an equal number of new supply ducts to both the upstairs and downstairs--lets say 2 new 6" ducts upstairs and downstairs. These new ducts will have powered dampers so they can be opened or closed. You also have to add powered dampers to two existing ducts both upstairs and downstairs. Now you have 8 dampered ducts. In the summer you close off 4 ducts downstairs via powered dampers and open 4 ducts upstairs. Same total air flow but now more is going where it's hot. Reverse the process for winter. Tie the dampers into the thermostats so it happens automatically.
Another solution is a 2nd furnace/AC for the upstairs or downstairs. That requires a utility closet (beware of noise), new equipment and lots of duct work. It's going to be much more expensive. Your house's construction/layout and current heating system design will be a determining factors as to which way to go.
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