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[MaverickM23]

That's exactly what I would like it to do, when the thermostat calls for heat I want the fan to come on. Then if the incoming line from the owb is lower than a certain temp say 140 the oil burner would also come on, so if the fire goes out or something we will have freeze protection

[RSI]

Ok, then I would use a 2 pole fan center or switching relay.

You would take the wires off the T T connections and connect them to G and RH on the fan center. (or could be T T depending on brand and model) Then you would connect one side of the relay (com and NO) to the T T connections in the furnace.

Then the other side of the relay connect to BLK wire going to the fan and limit to the com, and the R to the NO connection.

The Ranco can just be in series with one of the T wires or the B wire in the furnace. You would connect to com and NO in the ranco.

[MaverickM23]

Alright I'm following you so far is there a brand or model fan center or switching relay you would recommend? The only question I have is with the aqua stay I understand wiring in one of the t wires but would that be the hot wire and what would I use as the com?

[RSI]

There are two terminal strips in the aquastat. One is just to power it. The other is the relay. The wiring I mentioned was just for the relay side. For the power, just run from the incoming hot and neutral wires shown on the left side of the schematic.

The T wires are the low voltage thermostat connection. What I suggested would turn on the fan and short the T T connections at the same time. When those connections are shorted together, the oil burner will fire. The aquastat would keep them from shorting when the OWB is hot.

With it wired this way, you won't have the delay from when the oil burner fires till when the blower starts. That is because the hot air in the plenum was what turned on the blower.

Also, you will probably have to turn the temp up on the fan control if the heat of the heat exchanger causes the blower to start up. You could probably bypass it with the wiring but it is kind of a safety and should probably be left operational if possible.

[RSI]

Pretty much any DPDT relay should work. The fan centers need to mount on a 4x4 electrical box. Switching relays usually have their own enclosure.

[RSI]

Sorry about the multiple replies. I should have said DPDT or DPST will work in the last reply.

Something like a Honeywell 845A should work fine.

[MaverickM23]

Ok I think Im getting it. Im looking at a Honeywell R845A diagram and I see the T T terminals and also that it needs hooked to 120 power which I could get from where it enters the furnace. Then it has two areas that each have a to Power and Load . I take it those would be the same as NO and COM. My question is it mentions if using low voltage that I also need a separate transformer, so since Im using the one relay for the T T wires back to the furnace control I need that correct? Also the Ranco I got is for 120 only I think, therefore I cant break one of the T wires it has to be the black since that is a 120 line, is my thinking on this correct?

[MaverickM23]

Thinking and looking more at different switching relays and would a Honeywell ra832a do what I need? Couldn't I use the incoming thermostat on t t and then use the x x terminals to t t on the furnace that way I wouldn't need a transformer. And then I could use load 1 to power the fan and put the aqua stat in series on the black line ? Does my thinking make sense here

[RSI]

The ranco can switch any voltage up to 240v. It would work just fine on the 24v T T connections.

The RA845A would be better than the 832a.

[MaverickM23]

Alright thats what I will go with then, one last question I hope. On the relay that I attach to the fan you mentioned connecting it to the black going to the fan and limit and the red to the NO on the relay wouldn't I just want to break the red wire going to the fan motor so that when the thermostat calls for heat it will close that circuit and the fan will run?

[RSI]

You can ignore the NC and NO labels in the earlier post if you use the 845a since it is not double throw.
Here is is again modified for the labels in an 845A relay.

You would take the wires off the T T connections and connect them to T and T on the honeywell relay.
You would connect the line and neutral to both the Honeywell and the Ranco line connections. (ranco is labeled com and 120v)
Then you would run a wire from one of the T connections on the furnace to terminal 5 in the honeywell. Run a wire from terminal 6 to the C terminal in the ranco. Run a wire from the NO in the Ranco to the other T on the furnace.

Then run a wire from BLK wire going to the fan and limit to terminal 4 in the honeywell and a wire from R to terminal 3.

Just splice into the R and BLK wires.

[MaverickM23]

I drew it out and I think I have it all down, by splicing into the black and red I will be turning the fan on whenever the thermostat calls for heat. This will still function alright if I don't have the OWB going but it will turn the fan on before the plenum is hot if Im only using oil but what happens when the plenum gets warm enough and that switch closes but I already have the fan running? Sorry about all the questions, I just want to do it right and I know you are the guys who can help me do that.

[RSI]

If the switch in the plenum closes it won't hurt anything since it would be in parallel but it would keep the fan running after the thermostat quit calling for heat. Hopefully you can turn the temperature on it up high enough so that won't happen. You could disconnect the R wire from the switch so that won't happen. I just like the idea of having it there so if the oil burner is running and the relay failed it would still turn the fan on. If you just disconnect the R wire and leave the other wires it should still have the high limit there to shut the oil burner down.

[MaverickM23]

I follow you now thanks so much for all your help I really appreciate it.  I have a Honeywell 845a on the way and if  I run into problems I will post back, thanks for checking and keeping up with all my posts and questions

[MaverickM23]

Just an update but I put in the relay and aquastat as RSI described and the everything works perfect, I did remove the red wire from the fan control so it does still have the limit control but the fan is controlled directly by the thermostat. Fired the stove up and got it all up to 180 and hit the thermostat and the fan kicked on and he is drawing about 20 to 25 degrees off of the heat exchanger in the plenum, I have gauges going in and out of it, the only problem is that the Ranco temperature probe isn't giving a great reading. It is taped to the brass tee that the gauge is on and when the temp on the gauge says 180 the Ranco says 125 guess I need to experiment where to put the probe to get a better reading. But thanks again for everyone's help