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[Crow]

I have hopefully ( not likely ) the last thermostat question. I have a forced air oil furnace that is controlled with a low voltage t-stat(24v) and that goes to transformer to run the fan on high. I do not have air conditioning and do not have any plans to put in AC. Beside the t-stat on the wall is the manual switch to turn on the furnace fan for circulation but it is on low speed.

My question is this - can I hook up a new stat to maintain the oil furnace as is for back up BUT I would like to use low speed fan circuit when I am heating with the OWB? High speed on my furnace is loud and annoying! I am open to 1 new that will do multiple heat sources or two separate stats on the wall.  Just can't get my head around this and do not want to power both circuits at the same time if the OWB cooled off to the set point of the oil unit.

Currently the oil setup is there for backup only and is untouched. What I have done so far for heating this season is I have taken the panel off to access the oil furnace fan and put small fan in place of the panel and put it on a timer. It is working fine this way and is very quiet but NOT very professional looking.

Thanks for any information.

I will also mention that the oil furnace has a side vent system to work with oil fired dhw.

[RSI]

I am not sure if I got everything straight but it sounds like you want a thermostat to turn on the fan that your switch turns on?

If that is correct, I would just get another thermostat and put it in place of the existing switch. Connect one of the wires to the R and the other to the W on the thermostat.

[Crow]

Thanks RSI.
Basically yes. The switch turns on the same furnace fan just on low speed ( was relocated from the side of the furnace junction box ). The original t/stat is a low voltage to transformer to high speed fan......in a round about way. The switch beside the stat just interrupts the low speed circuit between fan limit switch and the fan motor.
So I'm assuming a line voltage stat is needed to replace the switch?

[RSI]

You have 120v running to the switch? If so, I would put a relay in it at the furnace and use a low voltage thermostat.

[Crow]

Yes I have 120v at the switch. So I will also require a transformer to power the coil in the relay or can I tap into the 24 volts from the original stat if I mount them side by side?

Or would a baseboard thermostat work? I found some at HD but have a minimum of 150 watt and I doubt low speed fan draws 150 watts.

[Crow]

Ok, forget the baseboard thermostat. I tried one in it last night. It is a two wire stat for electric heat with no minimum draw so I put it in place of the on/off switch. It turns on the low speed fan but after 20 mins the fan still running. So I don't know if it is defective or this type just not sensitive enough for this application.

[RSI]

I guess I forgot to reply again.

You should be able to tie into your existing transformer if you want to power the relay or you can just get a fan center relay with built in transformer.

If you want to use a line voltage thermostat instead, you can't use one that says it is for baseboard heater.

[Crow]

No problem RSI. I hooked it up with baseboard 2 wire stat on low speed fan and also tried on med/hi - could not satisfy the stat. So I used the oil furnace low voltage stat, 24/120v relay and transformer. It runs the fan ( I tried it on different speed terminals ) but again the heat is not enough to satisfy the stat.
 At least now I have the wiring part figured out but have more thinking to do about my system.