2 wire wifi thermostat?

[Rodbolt]

So I'm installing my infrared tube heater and I've purchased a Honeywell wifi thermostat model RTH6500WF. What I can't decipher is how to wire it. The heater diagram shows two wires, one is 24 volts AC and the other is signal to turn on heat. The thermostat does not show any instructions for a two wire setup but does require a 24 volt common to the C terminal. Can I simply run 24 volts to C and hook the signal wire to the W terminal? I'm hoping someone out there has gone down this road before. I've included a link to the Honeywell instructions and an image of the heaters wiring schematic. Thanks for your help!

http://www.wifithermostat.com/Resources/Pdf/RTH6580WF-User-Guide-English-French.pdf


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[mooseeater19]

The stat in the wiring diagram does not have a (c) common.
The wifi stat requires a (c) common

24volt transformers have a 24vac(r) and common (c) terminals.
The switch leg out of a thermostat is on the (w) terminal.
You need a 3 wire to the stat.

 

[rtcblc]

I installed this same thermostat and had to use one of the alternate wiring schemes. But not a 2 wire system. I'd just call there 800 number for tech help. Might be the easiest way to find out a correct answer. BTW-I'm pleased with the thermostat have had it for about 4 months and when it was -20 below recently it was reassuring to check on house temp from 350 miles away.

 

[Rodbolt]

The stat in the wiring diagram does not have a (c) common.
The wifi stat requires a (c) common

24volt transformers have a 24vac(r) and common (c) terminals.
The switch leg out of a thermostat is on the (w) terminal.
You need a 3 wire to the stat.

So is the common (c) terminal essentially ground? I looked at the transformer in my heater and one output wire goes to the 24 volt pin on the control module and the other output wire goes to a chassis ground. I have plenty of wires in the wall. Can I hook my "C" wire to that chassis ground and make this thing work?


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[mooseeater19]

So is the common (c) terminal essentially ground? I looked at the transformer in my heater and one output wire goes to the 24 volt pin on the control module and the other output wire goes to a chassis ground. I have plenty of wires in the wall. Can I hook my "C" wire to that chassis ground and make this thing work?


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Short answer , yes
I had a hard time seeing the wire diagram clearly so I wasn't quite sure where the common side of the transformer was going.

 

[nehog]

Please post the URL for that document, the image is not quite clear enough to read.

 

[Rodbolt]

Sorry for the hard to read diagram, here's the link. It's toward the very end of the document.

Mooseeater, the diagram does not show where the common goes, I figured that out by studying the heater itself. It sounds like running the C wire to the chassis ground should make this baby fly. Hopefully I can let you know later today!


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[Rodbolt]

Sorry, forgot to attach it.


http://www.superiorradiant.com/sites/default/files/files/products/manuals/SRP-Series-U-Manual.pdf

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[Rockhead261]

So is the common (c) terminal essentially ground? I looked at the transformer in my heater and one output wire goes to the 24 volt pin on the control module and the other output wire goes to a chassis ground. I have plenty of wires in the wall. Can I hook my "C" wire to that chassis ground and make this thing work?


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HVAC guy checking in.

It'll work long enough to make you feel good about it, but it will fail soon thereafter. C is not a ground. It's the common side of the transformer.

Don't ground the C terminal. This is not the old days where the thermostat was comprised of a mercury switch that would tolerate dirty voltage. You are dealing with sensitive electronics. You risk cooking your stat, the transformer, the system control board, or all three. Do it correctly and run a 3 wire.

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[mooseeater19]

Sorry for the hard to read diagram, here's the link. It's toward the very end of the document.

Mooseeater, the diagram does not show where the common goes, I figured that out by studying the heater itself. It sounds like running the C wire to the chassis ground should make this baby fly. Hopefully I can let you know later today!


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You want it connected to the c side of the transformer. when you say chassis ground if you mean where the wire from the common side of the transformer connects to the chassis , I think that is fine.
It's common to ground the c side of a transformer grounded .

 

[Rockhead261]

You want it connected to the c side of the transformer.

Correct.

when you say chassis ground if you mean where the wire from the common side of the transformer connects to the chassis , I think that is fine.
It's common to ground the c side of a transformer grounded .

Be careful. Just because the common side of the transformer might be grounded, I'll betcha a paycheck it's also wired directly to relays and boards and anything else that might require the common side of the transformer.

Don't use an earth ground as a conduit for a common. The thermostat requires C. Wire it to C.

 

[mooseeater19]

Correct.



Be careful. Just because the common side of the transformer might be grounded, I'll betcha a paycheck it's also wired directly to relays and boards and anything else that might require the common side of the transformer.

Don't use an earth ground as a conduit for a common. The thermostat requires C. Wire it to C.

correct
http://forums.mikeholt.com/showthread.php?t=153018

 

[tgb]

You'll also need to get into the setup on the t-stat and set it up for like a boiler or gravity heat or it will not work like it should because it will cycle too short. In all reality you should use a line voltage stat or a cheap bimetal stat with radiant for these type of systems or the flue pipe and tubes will start to rust out because they won't run long enough on a digital stat.

 

[Rodbolt]

HVAC guy checking in.

It'll work long enough to make you feel good about it, but it will fail soon thereafter. C is not a ground. It's the common side of the transformer.

Don't ground the C terminal. This is not the old days where the thermostat was comprised of a mercury switch that would tolerate dirty voltage. You are dealing with sensitive electronics. You risk cooking your stat, the transformer, the system control board, or all three. Do it correctly and run a 3 wire.

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Ok, let me clarify. The common side of the transformer goes to a stud on the inside of the metal box along with some other wires. I intended to run my third C wire to that stud. I'm not going directly to earth ground unless it is connected to the metal box also. I'm assuming that the C wire is simply needed to complete the 24 vac circuit to run the thermostat controls when the heater is off.


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[Rockhead261]

^ That works.

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[nehog]

Ok, let me clarify. The common side of the transformer goes to a stud on the inside of the metal box along with some other wires. I intended to run my third C wire to that stud...

That's the correct solution.

 

[Rodbolt]

Thanks for all your help guys! She's wired up and running!


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