Print

[MaverickM23]

Finished up my dads stove install but now need to tackle the thermostat wiring so the blower runs on a call for heat and the oil furnace only runs when it drops to a lower point. I have read numerous posts on this and saw these instructions that utilizes one thermostat and will do exactly what I need it to

Red to Rh or Rc with jumper between the two.
Green to G and W/E with jumper between the two
White to the W2 for gas furnace
Yellow to Y for cooling.

My only problem is that his furnace is older, and it only has a two wire thermostat, just an old round honeywell that runs to two terminals marked T and T, and the fan is controlled by a limit switch, there is no relay or transformer. My question is how can I accomplish a one thermostat setup with his current setup or does it need to be done with two thermostats. It doesnt matter either way if one will work great or if he needs two thats fine, but all the reading Im doing they all have more than two wires so do I need to convert his oil furnace to a 24v setup or will the old wiring work, also his furnace does not have any AC. I appreciate any help

[hondaracer2oo4]

When I had my old oil furnace the way that I figured out to do it was use a Honeywell RA89A1074 to turn the blower on in my furnace with one thermostat on the wall. Then I used a second thermostat on the wall to run the oil furnace and set it a few degrees lower then the thermostat for the blower. This worked ok,  but was not a great set up. If the oil furnace has to kick in, the blower fan is going to run and run and run because the thermostat for it is calling for heat. I never used oil unless it was a real emergency or something so it wasnt a big deal to me.

[mlappin]

Have mine set up pretty much like Hondaracer, I stuck with two for the greater differential, most of the ones I seen that could use a single thermostat the differential is only a degree or two before the secondary heat source is activated.

I also had mine set up so the gas furnace would kick on once a day to keep it “dried” out upon my father’s insistence, was much easier to go along than argue about it, I’ve done away with that as if the fan on the furnace is running it’s moving air thru it and should keep it dry regardless.

[MaverickM23]

So if I use two different thermostats what would the wiring look like? Could I still use the existing fan limit switch or do I need to upgrade since I only have two wires?

[hondaracer2oo4]

You will need someway to turn ONLY the fan in the furnace on. The fan limit switch makes and breaks the connection when the temp in the furnace hits a certain level. I wired my Honeywell RA89A in parallel with the fan limit switch. The problem with this set up is the fan will continue to run all the time if the owb thermostat is telling the RA89A to call for heat. 

[MaverickM23]

I did read yesterday where Slim said about putting an aquastat on the incoming line that breaks on temperature rise and then connect that aquastat to the furnace oil burner motor so it would turn off the motor and the fan and thermostat would act normally. Anyone done this before, I'm trying to find the part number for an aquastat to use but haven't found one yet

[sceptre74]

The aquastat is a 6006c 1018 by honeywell

[hondaracer2oo4]

Well funny you mention that. I guess this would work perfectly in your situation. I say funny because that is just what I did for my new set up. When the boiler temp drops to 140 the aquastat makes the connection. Don't bother with the mechanical aquastats from honeywell. Use a Ranco 111000 or Johnson A19. You can get the Ranco for $50 and it is much more programmable than the mechanical aquastats are. 

[MaverickM23]

Which one did you go with? I was looking them up and couldn't tell if they would work with clamping it onto my incoming pex or do you just tape the sensor to the pex. Also don't I want one that opens at a certain temp like a high limit it would open? I keep seeing SPDT but not sure if those would work.

[hondaracer2oo4]

You want the Ranco 111000-000. http://www.etcsupply.com/ranco-etc111000000-digital-temperature-controller-p-86.html  The single pole double throw means that it has a Normaly open(NO) and a Normal closed(NC) post. You would want to use the Normally open post. Then when the temperature hit a certain low point of whatever you set the Ranco to it would make the connection and allow the boiler to run normally until the incoming water reached the high point on the Ranco and killed power to the oil burner again.

[slimjim]

NICE DESCRIPTION!!

[MaverickM23]

Alright that makes much more sense. Thanks for all the help a Ranco is on the way. Now I just have to study the wiring diagram to see which wire I am going to break going to the burner. It is a Williamson R164 Lo Boy.

[hondaracer2oo4]

http://www.williamson-thermoflo.com/en/assets/pdf/en_w_thb_manual.pdf

That is the owners manual I believe for yours. Page 14 has the wiring Diagram. I think you should interrupt the black wire(Hot) Located at the bottom on the page going into the Burner Disconnect. That should kill burner power only for you.

[MaverickM23]

Here is the closest diagram I can find online  http://www.nortekhvac.com/literature/a864a.pdf its on page 12. I will get a picture of mine tonight to show you its on the back of the front shield but I forgot to take a picture of it.

[hondaracer2oo4]

Ok, I think your looking to break that Hot(BL) wire going to your burner mounted Jct. Box.