2 zone thermostat upgrade

Cosmic Charlie · 01-13-2008, 09:57 AM

Greetings to all. This is my first post here at DIY chatroom. I found this site while searching a question to do w/ my furnace's thermostat, and after looking around i thought I must join. You all seem like very friendly, knowledgable, and generous folks, and I hope I can add to the conversations in the various fields that I have experience in. My question today is, in my house I have two floors, each floor has its own thermostat, and the furnace has 2 circulating pumps, I assume that means 2 zones. While doing some cleaning and moving around of stuff the 2nd floor thermost cover was knocked off and lost. Can I replace the top floor thermostat w/ a programable one, and leave the basement thermo as it is. Both thermos are original to the house built in 1967. They are the kind that incorporate the lever that actuates a mercury switch. I purchased a newer digital one a few years back but I did not install it because of this question, and a compatability issue. I'm not sure if it is compatible. The old thermo has only a few wires (Im not sure at the moment how many) and the new has accomadations for many (not sure of count). Would you advise to replace both,? or would just the top floor suffice. The basement one only gets adjusted maybe a half dozen times a year. Thanks alot to any and all who reply. I look forward to becoming a useful and helpful member of your community. CC

bigMikeB · 01-13-2008, 11:11 AM

If the thermostat is only for heating you will only use the R and W terminals. There is no problem changing out only one t stat. The t stat you use must be powered by battery and not system, unless you add a resistor at the pump control relay to provide system power. If there are more than two wires, write down each wire as you remove it from which terminal on the t stat. The t stat is only a switch, so don't let it boggle your mind.

Cosmic Charlie · 01-14-2008, 06:54 AM

Thanks BigMike, much obliged. CC