Thermostat hook up

[Therealcrt]

I came to a job to re install a thermostat that got disconnected. There is a gas radiant heater that has a 2 wire that runs down to the area of where the thermostat is going. There’s also 120v from a a piece of MC hanging over here as well as a 120v to 24v transformer and a single pole switch. How do I implement this to work? The wires from the heater go directly to the thermostat but where do the wires from the secondary side of the transformer go? And how is the single pole switch involved

 

[ptonsparky]

120 volt to transformer with the switch in series of hot to the transformer.

Put the thermostat in series with the 24 volt to the heater.

 

[Little Bill]

I came to a job to re install a thermostat that got disconnected. There is a gas radiant heater that has a 2 wire that runs down to the area of where the thermostat is going. There’s also 120v from a a piece of MC hanging over here as well as a 120v to 24v transformer and a single pole switch. How do I implement this to work? The wires from the heater go directly to the thermostat but where do the wires from the secondary side of the transformer go? And how is the single pole switch involved

You need to know if the thermostat is line voltage or low voltage.

 

[ptonsparky]

You need to know if the thermostat is line voltage or low voltage.

This can't be a more basic control concept, even if line voltage.

 

[Little Bill]

This can't be a more basic control concept, even if line voltage.

Yes, I missed the fact that the heater was gas. I read too fast!

 

[__dan]

The thing to watch out for or be aware of, is more than one 24V source power for the 24V heater control circuit.

Possibly likely the heater is internally self powered for its 24V, external (field wiring) stat control circuit. So heater may be only looking for non powered "dry contacts" from the stat. This would be an old school common scenario. A non powered stat would work (not a Nest, separate issue).

Modern electronic stat takes steady power to run its cpu and display backlight. So three wires, hot, neutral, switched output. If you get the steady 24V from the heater, there's only one 24V power source, could be no issue.

But if you add a second 24V power source of your own, only for the stat, two 24V power sources could smoke the heater control board, and you have a scenario where you would have an interposing relay between the two, for dry contracts to the heater.

That would be what to look out for, the caveat. Research first, look at the heater and see what the instructions say for hooking up the stat. Be careful if adding a second 24V power source to the control circuit.

 

[hbiss]

Stupid question, is there a connection diagram or model number on the heater?

-Hal

 

[ptonsparky]

RTFM

 

[kwired]

Does this heater have a blower motor or is the only electrical load on the unit a 24 volt gas valve?

Units with blower usually will have the transformer within and you run 120 to the supply terminations and a 24 volt loop out to thermostat - if it even has terminations for that. Some potentially can just need the thermostat in the 120 volt supply line. I have to agree with RTFM if none of what I just mentioned is obvious to you.

 

[herding_cats]

The thing to watch out for or be aware of, is more than one 24V source power for the 24V heater control circuit.

Possibly likely the heater is internally self powered for its 24V, external (field wiring) stat control circuit. So heater may be only looking for non powered "dry contacts" from the stat. This would be an old school common scenario. A non powered stat would work (not a Nest, separate issue).

Modern electronic stat takes steady power to run its cpu and display backlight. So three wires, hot, neutral, switched output. If you get the steady 24V from the heater, there's only one 24V power source, could be no issue.

But if you add a second 24V power source of your own, only for the stat, two 24V power sources could smoke the heater control board, and you have a scenario where you would have an interposing relay between the two, for dry contracts to the heater.

That would be what to look out for, the caveat. Research first, look at the heater and see what the instructions say for hooking up the stat. Be careful if adding a second 24V power source to the control circuit.

Good advice. I've seen the damage from dual transformers. Most stats have Rh and Rc. This gives you the ability to use dual 24vac transformers. Post some data sheets and wiring diagrams?