[davsm55]

I am new to the list and just wanted to thank all who contribute to make this such a great resource.

Question:
I read the response from the following post "berces wiring two thermostats Jun 27, 2005, 05:54 PM" and wanted to know how to keep both upstairs/downstairs thermostats (hot) from losing there programming. Installing a double throw switch on red cuts power to the thermostats.

Is it possible to wire both thermostats with (W, Y, R, G) and just set the thermostat not in use to off? Would any problems occur if both were set to heat and the Thermostat simply closes the circuit when a set temperature is reached?

Any help would be greatly appreciated.
Thanks,
Dave

[labman]

Should work. If both both thermostats are on, the heat would stay on until both are warm enough to shut off. I guess if you set it that way, one could activate the furnace, and the other the A/C. Oops!

I guess if somebody wanted a switch, they could instal ones on the white, yellow, and green wires leaving power on to both thermostats.

[davsm55]

Thanks for the response... I completely missed the fact that you could accidentally turn on both the furnace and the A/C. It would work great as a dehumidifier;-)

Here is the situation... I use a wood stove that heats the downs stairs just great, but creates a 5-degree difference between the upstairs. At night (when the fire dies down) the kids rooms get a little too cold and I am looking for a way to have the heat come on based on the upstairs temperature.

I guess the full proof method would be to setup an electronic relay for W, Y, and G that buttons in both locations would determine which thermostat has control. Has anyone ever done this? Do any thermostat manufactures make such a thing?

Thanks again,
Dave

[labman]

I highly doubt you would find such a ready made device. If you did, likely it would cost a fortune. Another approach might be if both thermostats are digital and have the RH and RC contacts. I think it is the RC that powers the thermostat, and the RH is switched to the device selected. Run the red wire to both RC contacts, and to the common of a double throw switch. Wire the NCC and NOC contacts to each RH. The thermostats would have power all the time, but only the one selected would have power to switch to a device.

[davsm55]

Great suggestion! I will need to double check the wiring on my current thermostat (honeywell CT-3600). I know that R and RC are jumpered together, but I do not recall seeing a connection for RH.

I am considering moving the CT-3600 upstairs and purchasing the Honeywell VisionPro 8000 Thermostat (TH8110-U-1003) for the downstairs. In your opinion, is this a good choice?

Thanks again for the help.
Dave

[labman]

I just don't know enough about different thermostats to say. I am just a home owner that has ratted out some wiring problems, and learned some more here helping people figure things out. I would say, that if it doesn't use the standard R, W, Y, G, and B terminal identification, make sure you get directions you can understand with it.

I have seen very few problems here with any thermostat, other than figuring out the wiring.

[davsm55]

labman,
I checked my current thermostat (CT-3600) and it does not have an RH connection. Just R and RC, which are jumpered together.

Thinking out load:
A connection to R would allow switching for heating and another connection of R to RC would allow switching for cooling (reason for the jumper). That being the case (removing the jumper), if R was connected to both RC connections and I setup a switch to toggle between R connections you would still be able to turn on Heat from one thermostat and AC from the other. I guess I am a little confused about the wiring.

[labman]

R, and RC and RH usually are power in. Usually the red wire from the transformer runs to one. If there is a second, usually it is jumperd from the one the wire goes to. One way to sort this out would be to apply the red wire to both R and RC and see which one light up the thermostat. Then power that terminal at all times on both thermostats. Then switch the connection to the other terminals between the 2 thermostats. I guess we will eventually figure this out.