Harman p43 thermostat wiring with AUX oil heat

[lapoltba]

I have my new P43 installed and working beautifully. This weekend I wanted to wire it to my existing thermostat. It is a LUX TX1500Uc from Lowes. I really like the thermostat and it has an option to wire a 2nd heat source as aux, or "emergency" heat. It is currently hooked up to my boiler (2 wire connection, super easy).

I was hoping someone could take a look at this and see if they can make sense of it. I can't figure out how to connect things and keep the stove and furnace completely separate. I want the pellet stove to be primary and the furnace to be backup.

(broken link removed to http://www.luxproducts.com/support/TX1500Uc_ENG_WebManual.pdf)

 

[yrock87]

Use wiring diagram one. W1 for the stove and w2 for the boiler. Not sure if it will work as I think you need to connect up both wires with the Harman and you can't so that and still provide power for your boiler. The rh is your power, but there is only one power terminal on the heat side of your thermostat. You would need one each for the stove and the boiler to use them like you want.

I think anyways. I'm no expert on this.

 

[alternativeheat]

I have my new P43 installed and working beautifully. This weekend I wanted to wire it to my existing thermostat. It is a LUX TX1500Uc from Lowes. I really like the thermostat and it has an option to wire a 2nd heat source as aux, or "emergency" heat. It is currently hooked up to my boiler (2 wire connection, super easy).

I was hoping someone could take a look at this and see if they can make sense of it. I can't figure out how to connect things and keep the stove and furnace completely separate. I want the pellet stove to be primary and the furnace to be backup.

(broken link removed to http://www.luxproducts.com/support/TX1500Uc_ENG_WebManual.pdf)

It looks like the common from both systems goes on terminal C, then the other wire from one system on W1, the other W2. I'm sure there is programming for W1 and W2. This is assuming that both systems have just two wires of course.

 

[lapoltba]

I poked around with my meter a bit last night. The thermostat won't work as-is. It uses RH as the supply for both W1 and W2. So when the stove switches W1 it will be connected to the RH (24v Supply) of the furnace too. The W1 and W2 relays are not isolated, and I can't see any good way to modify it to be that way. I don't know how the stove would react but I'm pretty sure it wouldn't be good.

I don't think it is possible without a relay, but unfortunately I don't have a common coming from my furnace. I think I have a 24v relay in my parts bin somewhere, I may see what I can do.

 

[Don2222]

Hello

1st of all to make your pellet stove the primary heat connect one leg of the room probe to RH and W1
Since Rc is for air conditioning connection, jumper does not matter. You can leave it in or disconnect it.
I like this T-Stat because if dip switch 2 is up, it will set the T-Stat back to manual operation from the default of Programmable.

Now W2 is not auxilary heat, it is for stage 2 heat.
Stage1 and Stage2 heat is for very large areas such as commercial buildings where one boiler does not have enough BTUs to heat the area. When more heat is required, the stage 2 boiler is switched on.

Therefore if you want your boiler as an emergency backup, I recommend purchasing a second LTX1500u.

Set the pellet stove T-Stat to 70 Deg F and the boiler T-Stat to 60 Degs F

Also you should setup up a 2 deg F swing on the T-Stat for your pellet stove.

Just my 2 cents.

Click to enlarge

 

[lapoltba]

Wasn't worth the effort to run new wire to the furnace and figure out how to hack in a relay. FYI to anyone finding this later, this will not work with a standard thermostat. The W1 and W2 are switched to a common rail (RH) and cannot be easily separated. While this thermostat does support dual heat sources, it is not at all set up for use with anything other than standard heating appliances.

I opted to spend $20 on a new mechanical thermostat to dedicate to the furnace and I'll set it at 60F for emergency backup. Not short cycling the boiler all winter will save me a TON of oil!

 

[railfanron]

Yep. That's the way I do it. I have 2 Hunter programmable thermostats. One for each system. They're programmed to run at 70 for the pellet and 66 for the furnace.
Ron