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? Member Posts: 4
If I wanted to have two thermostats for upstairs and downstairs for a forced air heating system, would I just need automatic dampers controlling the air going upstairs that would be controlled by the upstairs thermostat? Please tell me how to install an upstairs thermostat with dampers. Where would the 24v and 120v wires go? Thanks.


  • Brad White
    Brad White Member Posts: 2,398
    Trouble May Be Lurking

    One of the limitations of warm air systems shows up with questions like this. The real right answer is, "it depends". The practical answer with many systems is, "tread lightly".

    With most forced hot air systems, you get one zone per furnace, one temperature to all rooms. If you "zone" with dampers, the best method I know of is what I call a "60-40" or "70-30" damper arrangement, whereby the volume of air is apportioned in those percentages to each zone but the furnace delivers the same air volume in total.

    These were principally developed for cooling systems to allow some high solar spaces to take what they need and not overcool, say, north spaces. In heating the application is similar. The air volume can shift between 30% and 70% side to side of the house for example.

    In other words, do not expect to positively shut down any one zone. To do so means your furnace will be deprived of airflow possibly below safety limits and will put out much hotter air to the space remaining "on".

    Absent modulating or staged fire and sophisticated controls, I personally would not go there.

    http://www.arzelzoning.com/ See this site for some ideas anyway. I have not specified them but they have been recommended in the past. They may have a way around my concerns.

    Hydronics such as a hydro-air system would be a better choice IMHO. Assuming that AC is a principal feature, the use of hot water coils in the ductwork to affect different zone comfort will not affect the fan coil unit (artist formerly known as furnace).
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • zeke
    zeke Member Posts: 223

    Since this is not an uncommon need, then maybe someone should make a damper controller that is controlled by the two room temperature inputs (thermocouple) ; a motor then continuosly drives the damper to change the apportionment (keeping the total cfm the same) until the two temps are equal, i.e. the error signal is the difference between the two. That would mean some sort of PID control as opposed to the fixed trial and error type which is not so hot. And the furnace would be controlled by a single thermostat in the main section.
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