Honeywell WiFi Smart (dumb) question


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Old 09-20-14, 09:42 AM
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Honeywell WiFi Smart (dumb) question

I have a HEAT ONLY system with ONLY two wires. There are also only TWO terminals at the furnace, as far as I can tell as the block where they are is marked THERMOSTAT.

At the thermostat, one of those wires (white) is connected to the W terminal. The other (red wire) is connected to the RH terminal with a jumper going to the RC terminal. That's all there is.

It appears that every schematic I see on the Honeywell site for these things requires either additional wires or possibly a 24v transformer. Obviously I'm not sure how to handle this. I'd rather not run another wire up from my basement.

Any thoughts would be appreciated. Thanks.
 
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Old 09-20-14, 10:02 AM
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Follow up. A Honeywell techie just told me every WiFi unit would require a 24v transformer under my circumstances. Within five minutes a buddy of mine told me he has one successfully running off his old 2/wire system without a transformer, same as I currently have for my old non-WiFi therm. So it's a mystery to me. I just don't want to by a new thermostat I can't use.
 
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Old 09-20-14, 11:23 AM
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You have a few options...

Post the make and model number of your furnace. Some pictures may be required if it is over 20 years old or it isn't a major name brand unit. It may be possible to pull wire from your furnace to the stat to add the 24 volt common required by wifi stats.

If pulling wire from any 120 volt plug is an option, an external 24 volt transformer can be used to provide power to the Rc and C terminals, and you can connect the 2 existing wires to R(h) and W.
http://www.amazon.com/Elk-TRG2440-24...lt+transformer


If pulling wire is not an option you can consider a wireless thermostat and install an Equipment Interface Module near the furnace.

Another option would include power stealing thermostats. The Nest thermostat is able to operate using power stealing (as well as using a common wire). Power stealing is the least reliable option.
 
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Old 09-20-14, 01:13 PM
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I think the Elk transformer you sent is the ticket. That seems a great option.

Thanks very much. Ken
 
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Old 10-04-14, 07:09 AM
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Still got a question about transformer + wifi thermostat

I bought an ELK transformer as advised in this thread to run two wires from that (using the two AC terminals and not the ground) to a new WiFi thermostat's R and C terminals. NO problem so far.

The current old setup has ONLY two wires from the furnace going to the old thermostat. One goes to the W terminal, the other to the RH terminal which has a jumper connected to the R terminal as well. The problem is that the NEW thermostat has a W terminal but DOES NOT have an RH. Instead there's an R (already connected to the transformer as mentioned above and also has an RC terminal. Is the RC where the 2nd wire from the furnace goes?

This is an old heat only furnace. Thanks very much.
 
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Old 10-04-14, 07:49 AM
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Yes, the new transformer will use the Rc terminal and you do not want a jumper between R and Rc at the stat.
 
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Old 10-04-14, 09:23 AM
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My apologies if I haven't been clear BUT, your answer did not answer the question of which terminal on the new stat the 2nd wire from the furnace goes to. TO repeat (sorry), there are ONLY two wires from the furnace, one of them goes to the W terminal. The other CURRENTLY goes to the RH/RC bridged terminal on the OLD stat. As there is NO terminal RH on the NEW stat, I don't know where to connect it. What's on the NEW stat is R and RC and I'll be using RC for the transformer. SO, should I use R for the furnace connection? If yo need any info on photography, I'm your answer man. For this I need you. Thanks again.
 
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Old 10-04-14, 09:44 AM
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The furnace connects to R and W.
The external transformer connects to Rc and C.

Name:  Transformer external.jpg
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Last edited by Houston204; 10-04-14 at 04:19 PM.
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Old 10-04-14, 09:53 AM
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I am grateful. Truth is I've helped many aspiring photographers...it feels good.
The diagram is perfect. I MUST ask this, however. Somewhere along the line in the last couple of weeks while waiting for the stat and transformer someone in thew forum said that the ground on the transformer is not to be used, just the two other terminals. "No ground" didn't make sense to me. I'll hook it up however you say.
 
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Old 10-04-14, 09:58 AM
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The transformer is grounded but you will not run a third wire from the transformer to the stat for ground.

The stat doesn't have a ground terminal and the housing is plastic.

I can't read the labels on that transformer from the picture. If you could post from left to right the terminal labels I will correct the diagram as needed.
 
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Old 10-04-14, 10:12 AM
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Sure, left to right.....AC - GND - AC
 
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Old 10-04-14, 10:36 AM
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Again, appreciate the information...thanks very much.
 
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Old 10-04-14, 11:20 AM
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I would have liked to see 24VAC, Com, and Gnd.
I would measure AC to AC with a volt meter to verify 24 volts.
 
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Old 10-04-14, 01:17 PM
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Rats, NOT that I understand these things, but I do have a volt meter and it reads 28v.

Bad mistake to use the transformer?
 
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Old 10-04-14, 01:27 PM
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28 volts is a good reading. The transformer is fine.
Was this measured from AC to the other AC terminal?
 
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Old 10-04-14, 01:40 PM
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Yes, that's what I did. I've got to leave here and won't be back for a few hours if there's anything else but I think we're done. Again, I'm grateful...so's my wife. Ken
 
 

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