Can this be used for "C" wire to the digital thermostat?

[JasonM]

DonL, it works fine without the battery. In the manual, it says that the battery is optional and backup only in case of power failure.

Since this new thermostat is not programmable, there is not much setting lost in case the power goes out.

Thank you.

 

[clocert]

From the manual, you already knew your T-stat has the (C) power option. why are you still asking the question here.

 

[Sponsor]

 

[DonL]

From the manual, you already knew your T-stat has the (C) power option. why are you still asking the question here.

I was the one that asked.

Jerry Cleared it up, and Jason confirmed.

I build backups for my electronics, that do not have them, I live in the woods. Battery backups are great, I never would disable one. Just me and knowing how electronics with a CPU can crash in a heart beat.

 

[capecod12]

We check houses for people with new gas furnaces, and digital thermostats, who are not here for months in the winter. Just recently we had two furnace shut-downs, and the power had NOT gone off in our area. Turns out that they have new digital thermostats, and the batteries had gone dead. Luckily we caught them before the houses froze up, it was in the single digits outdoors.

We managed to save their houses! But what the heck is going on???? Are these new thermostats not hard wired into the wiring, so that a doggone battery can cause a total failure in a new heating system, and freeze up a house???

I am astonished that an entire heating system is dependent on two AA cells?
People with Generac generators which come on automatically in a power outage, could still have a heating system shutdown???

Is this true? Then why arent these thermostats hard wired into the house electrical system to prevent this idiotic issue??
Yeah, Im only a grandmother, what do I know,,,,,,but I am very very concerned with this problem, 2 houses on one street with this issue within a month.

I have more info as of tonight,, I will post this info tomorrow, as its late and I am still very angry about this problem.

 

[Reach4]

Is this true? Then why arent these thermostats hard wired into the house electrical system to prevent this idiotic issue??

No-- not if the thermostat is properly wired (with the C wire connected).

 

[capecod12]

I wonder how many are improperly wired, and are dependent on those 2 little batteries while the people are away for the winter?
I talked with our daughter who's husband consults for an insurance company who specializes in house freeze-ups, and a good percentage of the claims are exactly what we are dealing with here, 2 dead batteries and the entire heating system shuts down.

So what should all these people do? How to get the info out if the companies who install these thermostats, are NOT connecting the C wire?
I actually called Honeywell(our new thermostat), and they admitted on the phone that if the C terminal is not wired properly, that this would happen. Advised to have it changed by an electrician. Im not going to do it myself, so I called our installer to have them come back and fix it properly.

They probably think Im a pain in the butt, but when something is this important, then things should be fixed. I doubt that the young electrician who installed ours, even knows about this issue.

 

[Reach4]

How about pull the batteries and make sure the thermostat still works.

 

[capecod12]

It doesnt, I tried it.
Here is the issue well explained,
http://jonrosensystems.com/2014/01/...to-the-destruction-of-your-home/#.VRKu4jvF9HF

 

[Reach4]

It can be easy to run the C wire. If worst comes to worst, put in a thermostat cable with more conductors. If you have access to the path, running a new 8-conductor cable should be relatively easy. Sometimes you can re-purpose another wire. How many conductors are in your cable. Do you you have AC, and do you need to have the fan run upon command? Is it a 2-stage furnace and the thermostat supports that? Those things take a conductor.

They make it pretty clear in the installation instructions that you need the C wire to not eat batteries.

Here is another thought: you can have a second mechanical thermostat across two of the wires. Set it to maybe 45 degrees F. If the electronic stat fails open, the mechanical one will call for heat. You would put that in a hidden place but one that will get cold if there is any danger of pipes etc freezing.

You could also get a "construction thermostat". Those are small and are set to close at a fixed temperature. That would be your failsafe. Wire it across the right two wires, and it sets a minimum temperature.

Incidentally, I put in my WiFi electronic thermostat when my mechanical thermostat failed open so I did not get heat. It used a mercury vial!

 

[capecod12]

Thank you for this info, we will see what we will choose to do.
What you described is a great work-around. Its very important to have a fail-safe situation.

A friend is getting me some of those old Honeywell circular mercury thermostats. People throw them away.
We dont have AC and its not a 2 stage furnace.

In our situation, our house would survive, as when we put the new gas furnace in, we kept our dear old Metromatic oil furnace. We use it as a back up.

 

[Reach4]

Your backup thermostat would go across the R and W terminals. http://www.behvac.com/troubleshooter41.htm

If you have 4-conductor cable run, and have a Y wire but have no AC, you could re-purpose that wire at both ends to use as a C wire.

You need to keep the R and W, and you need the G wire if you need the fan control to work. If you did not run the G wire, the fan would still run when the plenum was hot.

 

[Jadnashua]

It probably goes back to the time when all you had was a simple mechanical thermostat and all it needed was two wires - a way to connect the 'hot' lead to the relay to turn the furnace on. There was no need for extra wires, and a simple 2-wire cable is cheaper and easier to run. Electronics and the desire for more creature comforts means today, you need a much bigger cable to make everything work right.

 

[capecod12]

This is very interesting, I certainly have learned a lot from you here.
The fan is a variable speed, the furnace is a Carrier, so I want it all to work perfectly.

 

[JerryR]

Here is another option to use an simple wall wart AC transformer to provide external power to a thermostat.

 

[capecod12]

Thank you muchly for these great videos. I found one which explains our exact Honeywell t-stat.