Another thermostat question please

[beagledog]

Hey all. I have a two wire thermostat currently and plan on adding another one to turn my oil furnace fan on when called for. I have no AC. The question is, when I am looking at my honeywell furnace where the thermostat wires lead, I'm not seeing any of the terminal indicators like R, C, Y, W, G, O, B or similar. My two wires from my t-stat go to two terminals labeled T which I assume is for thermostat. There are two more wires on the board that come from god knows where(inside conduit) and attach to two terminals labeled F which I assume is fuel. I'm reading old posts on this site that say you can use the existing 24 volt service to power the extra thermostat and cross this wire and this wire and so on, but I don't seem to have the red and green that I need to cross. Any help please. Thanks in advance.

 

[Billy_Bob]

The color of the wires is not important. Actually anyone could use any color of wires they choose!

So don't go by wire colors, rather by how the circuit functions.

If you have just two wires going to your thermostat, then there is probably just an off and on for those two wires. (Connected or not connected.)

And probably if connected, they turn on your furnace.

And if you had two thermostats wired in "parallel", then if either one detected it was cold, then the furnace would go on.

Or if you had both thermostats wired in "series", then both thermostats would need to detect cold for the furnace to go on.

How do you want this to operate?

 

[beagledog]

My plan was to leave the existing thermostat around 5 degrees lower than the new thermostat and have the new thermostat only turn on the blower. If the fire were to go out, the fan would continue to run until the 5 degree difference was reached, and then the old t-stat would turn on my oil furnace. At least I thought this would work. Thanks.

 

[beagledog]

Also, I have a 24 volt transformer that came with my owb so that you could run a t-stat wire to the back of the owb if your installation required you to. I could remove this and put it in the basement to power a t-stat for my blower fan if I had to, couldn't I?

 

[beagledog]

The transformer has two terminals marked p and c on top. If anyone can suggest how to utilize this with its own thermostat, that would be great also. Thanks

 

[coyotencuttin]

you are gonna need the control on your furnace to have a terminal to control the blower. usually a g terminal. that terminal should be connected to the furnace thermostat. if the existing stat only has 2 wire connections you are gonna need a new/different stat that also has a fan terminal on it.g treminal. if the owb has its own transformer you are gonna need to make sure that you keep the low voltage separate from the furnace 24 volt power. the stat that came with the boiler should probably be utilized to run the owb to either run the circ pump or open close the damper.i'm not sure how your particular owb works. if you run the fan with the furnace stat then the owb stat can just operate the owb and if the owb goes out/run out of wood all the control will still be at the primary stat. hopes this helps. harold

 

[beagledog]

The owb has its own stat and transformer. The transformer I mentioned is for if you wanted to run a stat wire out to the owb from inside which I don't...so that transformer is going to be unused. So does that fact that my furnace doesn't have a G terminal mean that I'm not going to be able to wire a stat to the fan alone? I'll buy the new stat with as many wires as I need to make it work...I just don't know where I'd hook them all up as my furnace has so few terminals. Maybe the limit switch for the fan? Thanks for all the help.

 

[Billy_Bob]

Your going to need to post a wiring diagram of your specific furnace model or a link to a wiring diagram of your furnace (manufacturer). Also pictures of the wiring inside the furnace would help.

Fans are higher voltage house electricity (120 VAC), and thermostats and their associated wiring are low voltage rated.

So to do this safely, there would need to be a transformer and a relay inside your furnace controlling the fan. Then you could probably parallel connect another thermostat to the low voltage relay control connections (if you have that). You would need to run two new wires from your new thermostat to the furnace. And these would be connected to the temperature portion of the thermostat (not fan switch). You could use a simple cheap thermostat.

So the second thermostat would turn on the fan only.
The first thermostat would turn on the heat and the fan as it has been doing.

You would leave the wiring to the first thermostat as is.

How relays work...
http://www.howstuffworks.com/relay.htm

 

[beagledog]

Here are links to the pics. In pic one, the 2 upper left wires are coming from the t-stat. Both terminals are labeled T. The 2 terminals to their right are labeled F.

In the second pic is my fan limit switch.

Sorry you can't read the writing but the blue wire on the left comes out of "load fan line" and then goes all the way to the fan motor. The red wire comes out of "load limit line" and heads into the conduit. The black comes from the other end of the "load fan line" hole and heads into the conduit as well. In the center of the switch is a little tab and it says "remove for low voltage" The white button on the lower left is for putting the fan in manual(in) or automatic(out).
I'll try to untangle the birdnest and find where these other wires go. Thanks alot for taking the time to look.

 

[coyotencuttin]

the easiest way to do what you want to do is to push the little white plastic button in on the second picture. that is the manual override on the fan/limit switch. runs the fan constantly irreguardless of burner operation. the next best way to run the fan is to add a fan center to the furnace. it is just like adding an add on a/c to the furnace, it allows the function of using 24 volts to bring the fan on from the stat. you are also going to need a split subbase stat and 5 conductor t stat wire . to me its not a talk you through installation to add the fan center. i don't like to do it much inperson.you could wire a switch to power the fan usong 120 volts but i am strongly against doing so. if you are going to mount a stat to operate the owb, pushing the white button in qualifies as easiest and cheapest option. harold

 

[beagledog]

What would be the problem with wiring a 110 volt stat to the power right at the furnace fan? This seems the simplest to me...is there something wrong with my thinking here? A new 110 stat, wires run down and spliced in at the fan and the original stat and control will still be fully functional. Thanks

 

[coyotencuttin]

After rereading the posts , I see what you are after. Yes you can add the line voltage stat to run the fan.you are gonna need to run the voltage parrallel to the fan/limit switch. That way the fan would still operate with or without the line voltage stat calling for heat.also just make sure you pick up voltage also from the furnace so as to not get a different leg of voltage and possibly send 220 volts to the blower motor. But yes it would work. Harold

 

[beagledog]

Fantastic...that's just what I wanted to hear. Thanks for all your help.

 

[beagledog]

Just an update on how this ended up. I bought a line voltage thermostat (110v) and spliced it into the hot lead right at the blower motor for the furnace fan. Put my fan in manual at the limit switch and presto...it only runs when the new stat calls for heat. The oil t-stat is still fully functional and set about 10 degrees cooler. Thanks again to all for the help