How Do I Connect This Wire?

EBEBRATT-Ed

Yeah, I think it is a good idea as well.

Chapter 1. How to get a common wire to a Nest

Chapter 2. Taco Switching relay wiring

Chapter 3. How to flare oil line tubing

Chapter 4. All about TIGER LOOPS

@Larry Weingarten has a few books I am sure he could help you avoid some pitfalls

Larry Weingarten

Hi @EdTheHeaterMan, @EBEBRATT-Ed is right. I'm working on my third book now, so can certainly show you where some of the book biz ropes are. There are a number of authors who frequent this place. Mix up technical, stories, and humor, and you'll have yourself that bestseller. It will be another reason to have spent so much time and effort to learn this stuff. 😻

Yours, Larry

EdTheHeaterMan

@Larry Weingarten… I started to do just that. I am going to use the title you suggested. "Keeping the Smoke In".

Larry Weingarten

@EdTheHeaterMan , Wonderful! It might need a clarifying subtitle. Otherwise Bill Clinton, and "not inhaling" come to mind. 🤪

Yours, Larry

EBEBRATT-Ed

It is sure to be a NYT best seller!!!!

EdTheHeaterMan

https://forum.heatinghelp.com/discussion/comment/1783725#Comment_1783725

This is a problem with many gas steam boilers when you want to add a smart thermostat that requires a C wire Connection. Here is another Boiler made by Dunkirk that should use an isolation relay.

I find that the Packard FC90113 is one of the least expensive combination transformer/relays available and is very easy to use for the isolation relay.

Steamhead

@EdTheHeaterMan , following the link and enlarging the third pic, we can see that unit is made in China. So it won't be inexpensive for long………………

EBEBRATT-Ed

I noticed on the link that the Packard and the White Rogers look identical with the WR about $2 more. Both made in China.

The Honeywell is almost double the price……….country of origin…….CHINA

Steamhead

So none of them will stay at that price for long.

EdTheHeaterMan

@Steamhead & @EBEBRATT-Ed… You can purchase a "Fan Center" from a boiler manufacturer for over $100.00 and find that it is identical to any of the lower priced items. The "rub" is that the wire colors are different. Since many plumbers (and even some electricians) are not that good at control wiring, changing the colors of the wires make it difficult for some to adapt the identical low cost part with the expensive "Factory Authorized" part.

Regardless of the political climate. The boiler manufacturers will always have an excessive markup for the generic parts they sell. That is why they have slight changes in them. Just so you won't try to buy the lower cost generic parts. That is the reason I like Crown by Velocity Boiler Works over Weil McLain. Crown will tend to use standard parts for their boilers rather than modified "OEM" parts.

When the Tariff's kick in, you can see the OEM fan centers go from 100 to 200 while the generic will still cost less than 50.

EBEBRATT-Ed

If they go up that much a transformer and a RIB will work and nut much more work to install.

Wasn't there another relay like a RIB that had a transformer built into it? Someone posted it last year I think. But maybe the trans is to small for a Nest.

EdTheHeaterMan

I think that RIB is a Made in USA product and they also have 50 VA and 75 VA transformers at reasonable prices. So my post for that Packard fan center may become obsolete in a few months.

EBEBRATT-Ed

I like Ribs because the little red light tells you it's working.

EdTheHeaterMan

C wire on smart thermostat. Where do I connect the R. (Rc or Rh).

Here us a successful post from the other day. Boiler owner wanted to connect the fan switch form the old furnace to circulate air. No AC installed yet, so he connected Rh and C to the wrong place. After I analyzed this problem I came up with this and the OP got it working.

https://forum.heatinghelp.com/discussion/comment/1860247#Comment_1860247

According to what I have read about most smart thermostats and specifically the Ecobee information online, Rc and C must be connected to the same transformer to power the thermostat. If you connect Rh and C the thermostat will not get power. If you connect Rc from the Ecobee to the transformer of the duct system control transformer, and connect C from Ecobee to the boiler control transformer, you will not get a completed circuit.

See how this R and C connections are going to two different transformers? That not going to power anything. The source 24 v. transformer is different from the Return Path transformer. No completed circuit here

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The smart thermostat's (CPU) central processing unit (computer) gets power from Rc and C. So this next diagram will also not operate the thermostat.

The reason this wiring configuration will not work is the Rc does not have power to operate the thermostat's CPU.

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The correct heating only wiring for most smart thermostats is this diagram

With this wiring configuration there is power to the smart thermostat's CPU. Now the brains of the thermostat can figure out that the thermostat is connected to a heating system that needs Rc to W in order to make the boiler or heating only furnace to come on.

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The only time you need Rh in most smart thermostats is when you have an air handler system that might be cooling only and a separate heating system like a boiler for hot water or steam heat. Then you need to isolate the two different transformers. That is the function of the Rh terminal on any thermostat. Make sure the Air Conditioner's 24v. control transformer does not connect to the heater's 24v. control transformer. This diagram illustrates that point.

The Blue and White areas represent the air handler or furnace side of the thermostat. Once you connect a wire to the Rh terminal on a smart thermostat the thermostat's CPU recognizes that and creates a kind of a firewall to separates the heating only section in the Red area from the rest of the system in the blue area, within the thermostat.

Without the Rh wire connected then the thermostat's CPU does not form the firewall and the Rc will be able to operate the heat burner thru the W (and W2 if needed) like you would find on a regular Gas furnace, along with all the cooling and fan systems/relays.

Edward Young Retired