House Thermostat Question

[Robert11]

Hello,

Trying to understand, a bit, about how these components "play" together.

Have a typical forced hot water home system; gas fired.

Was wondering about the Honeywell Thermostat I now have for it. It's a RTH 5100B 1009

Two wires, only, going from unit to the furnace control box on the furnace's side.

Pretty basic, and probably dumb, questions, but if anyone could help me out in understanding this would be most appreciative.

Questions, please:

a. I guess that the sole output of the thermostat unit when calling for heat is to simply close a single pair of contacts. True ?

b. If so, does it have a "small" mechanical relay inside ? Or does it use a solid-state closure ?

c. And, that the 24 V dc is provided, probably, by a transformer in the Honeywell control box mounted on the side of the furnace, and Not by the Thermostat ? True ?

Thanks for help, R.

[Dean Hoffman]

There's a website called How Stuff Works.

[trader_4]

You ask these same questions a week ago and they were answered.

Yes

All the ones I've had used a relay, you can hear it click. Some are solid state, the Nest for example is, or at least was. They had a lot of problems with that part of it in the early days.

Yes, but it's 24V AC. Most electronic thermostats typically have batteries to power their electronics. Some steal power from the 24V transformer when the call for heat is off. Some have the option of being powered normally from the 24V transformer if you have an additional wire back to the transformer.

[hubops]

https://usermanual.wiki/Honeywell/HoneywellRth5100BInstallationGuide803268.895951082/html

[Clare Snyder]

Generally the thermostat runs on 24 volts AC from the transformer

[Tekkie®]

Robert11 posted for all of us...

Yes