Picking the right thermostat.

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Old 01-26-20, 08:03 AM
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Picking the right thermostat.

Morning, I just moved into a new house and am looking at getting a smart thermostat. I grew up in a house with just oil heating and AC's in the rooms so a swap was easy, but now I have a CA system as well as oil. I just want to make sure I buy the right thermostat and know if I need to run a C cable. Here's what the guts of the older one look like.
 
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Old 01-26-20, 11:10 AM
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Welcome to the forums.

You have two systems controlled by that thermostat. Two distinct cables.
Cable 1............... The heat is on red(Rh) and white(W).
Cable 2............... The A/C is on red(Rc), green(G) and white(W).

You absolutely need a C connection and it comes from the A/C air handler.
Check and see if there are any cut off wires in the A/C cable.
 
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Old 01-26-20, 04:39 PM
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Thanks for clearing that up for me. As far as wires around the AC unit I couldn't find anything that looked cut or out of place. It seems everything is hooked up right.
 
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Old 01-26-20, 04:50 PM
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You have two options.....
1) run a new cable down to the stat. (recommended)
2) you can lose control of the blower at the thermostat and use the fan wire as the C wire.
With this method.... there is no more "FAN ON" mode.
 
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Old 01-26-20, 06:04 PM
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Sounds good, sorry if the info I was giving wasn't nearly helpful enough. By oil heating I mean that I have furnace and baseboard heating. And the cooling is a Goodman A24-00. You wouldn't happen to have a link to a wiring diagram so I can put that C wire in properly?
 
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Old 01-26-20, 08:25 PM
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C is the big light gray wire under your thumb in the picture that you posted.

The AC condenser connects to stat Y and air handler C so you will end up with 2 wires connected to the air handler C.
 
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Old 01-26-20, 09:19 PM
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You have a boiler and baseboard heat..... A furnace is hot air. A boiler is hot water.
 
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Old 01-27-20, 06:14 AM
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You have just one thermostat for heat? No others in other parts of the house?
 
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Old 01-27-20, 04:56 PM
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It's a ranch so there's just the one.
 
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Old 01-27-20, 05:13 PM
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So have we helped you make a decision ?
Any more questions ?
The Ecobee 3 is a good choice...... Honeywell T6 is another.
 
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Old 01-27-20, 05:27 PM
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Yeah you guys have been a great help thanks a ton. I was looking at the ecobee3 before I took to the forums so I'll go with that and hopefully not blow up the house in the process
 
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Old 01-30-20, 05:32 PM
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Went about as well as expected. Any idea where I can attach a C cable?
 
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Old 01-30-20, 06:20 PM
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In your picture in post 3...... that white/gray wire in your thumb is C. You can connect right there.
 
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Old 01-30-20, 07:09 PM
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Tried that, didn't give any juice to the stat.
 
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Old 01-30-20, 07:32 PM
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Forget I wrote that. So I can add a third wire to where the gray and white twist together? Or is one of the white cables coming out of the wall supposed to be C?
 
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Old 01-30-20, 08:59 PM
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In your picture..... there is a three wire cable. This cable goes to the stat. If it's still being used..... R (red) goes to orange color. G (green) goes to yellow and white goes to red of the A/C condenser.

How did you get C to the stat ? One wire.... new cable... ?
 

Last edited by PJmax; 01-31-20 at 04:37 PM.
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Old 01-31-20, 04:09 PM
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I used the white wire that's connected to the thick grey cable, because from what I understood was that since it was connected to the grey cable, it would act as a C. But obviously that didn't work. So can I just add a third cable to the grey cable and white wire twist and use that as my C? As I was going over the ecobee instructions it seems that the main issue I'm coming up with is that I have a dual transformer system. I just can't figure out where the C wire is supposed to start at the A/C.
 
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Old 01-31-20, 04:18 PM
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Ok..... let's just take a step back. From what you've said and what I see in your pictures you have three wires between the air handler and the thermostat. You need a fourth wire.

How are you going to get a 4th wire to the thermostat ?
 
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Old 01-31-20, 04:26 PM
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I was planning on snaking it from the hole in the wall to wherever the C needs to start from. I know easier said than done, but that's the plan. I've run ethernet cable through the house so I know it's a pain but doable.
 
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Old 01-31-20, 04:33 PM
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Ok.... so that wire you are going to run connects to the C of the thermostat and the gray wire at the air handler.
 
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Old 01-31-20, 04:35 PM
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Ok, so just add a third wire to the twist cap at the end of the grey wire and pop the other end in C, that sound right?
 
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Old 01-31-20, 04:38 PM
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Yes..... that is exactly correct.
 
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Old 01-31-20, 04:55 PM
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Thanks for being so patient with me on this lol. I'll let ya know how it goes.
 
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Old 01-31-20, 05:03 PM
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Not a problem. ......................
 
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Old 01-31-20, 07:25 PM
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Sweet victory. Again, thanks a lot!
 
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