New T-Stat but not enough wires


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Old 09-16-14, 11:37 AM
J
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New T-Stat but not enough wires

I currently have a single stage T-stat, but a newer 2-stage conventional furnace. I would like to upgrade my t-stat to take advantage of the 2-stage, but I am short on wires.

Right now there are only 4 wires, but I need 5. My options as I see them at the moment:

1) Honeywell's non WiFi or Zwave T-stat (RTH8500D) does not require a common wire and can be run off of batteries. This would solve my problem except I think I want the WiFi (or Zwave if I implement home automation in the future).

2) Try to run a new set of wires from the furnace. This won't be trivial in my house, unfortunately.

3) I'm not sure if this is possible, but could I wire in a separate 24V supply off an existing circuit near the T-stat using some sort of transformer?

Any advice would be appreciated!
 
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Old 09-16-14, 05:04 PM
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To take advantage of two stage and use a common, you'll need 6 wires. (w2 must be connected)

Pulling new wires is always best, but I've done a two-stage battery powered stat over 4 conductors with add-a-wire. (Venstar Inc. - Add-A-Wire ACC0410)


There's also fast stat (FAST-STAT - Wiring Extenders and Thermostats Controls).
 
  #3  
Old 09-16-14, 05:35 PM
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Thanks for the response, Muggle. I do not have any cooling, so I believe I only need 5 wires (correct me if I am wrong):

R: Heating power
W: 1st stage heat relay
G: Fan relay
C: Common
W2: 2nd stage heat

Regardless, if I ran a new wire I would run 18/7 just to eliminate any problems in the future. I'll have to look more closely at how the current wire is ran now, but it would involve some work.

Seems like the easiest option right now is to get the battery powered stat that supports 2-stage. If I end up wanting a wifi or z-wave stat in the future I would have to run a new wire. I think the "FAST-STAT Common Maker" would work, too, without having to run a new wire.

Thanks again!
 
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Old 09-17-14, 08:43 AM
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Yah I would go for a battery stat, unless you want to add cooling down the road. That's what I did, but with cooling. I think the rth8500 can be operated on battery or common.
 
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Old 09-17-14, 09:43 AM
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Yes, the RTH8500 can be operated on battery or common. I just put in an order for one. It'll get me through this winter being able to utilize the 2-stage capability of the furnace, which is my main objective. If I end up wanting wifi or z-wave control, then I'll add a wire.

I took a look at my wiring yesterday and it wouldn't be too bad, just having to fish a wire through my garage ceiling. On my list of projects is to add some more lighting to my garage, so while I am fishing wires for that I'll probably run a new wire for the stat.

Thanks again!
 
 

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