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[HillBillyEngr]

New to the board and a Newb at outdoor wood furnaces so please bare with me. I purchased a house about a year ago and after a 2k oil bill for the season my wife and I knew we had to do something other than oil. First off my house has two independent heating systems the heat pump (old portion) and the oil furnace (new portion) these units completely disconnected from each other. My plumbing is complete and pressure checked. I have 3 Circulations off my outdoor wood furnace (Mahoning 300)- 1 for my old portion (heat pump) with a 16x16 water to air heat exchanger and 1 for my new portion (oil furnace), and another for my domestic hot water heat exchanger. The circulations will run 24/7, to control my heat the thermostat will need to control the blower. This is where my problems start. I think I have the heat pump side figured out. Two thermostats the heat pump will be turned to fan and the second thermostat will break and make the green wire to turn on the blower thus hot air from the heat exchanger. My problem is the oil furnace side.

My oil furnace has 2 wires running to it red and white. From the way I understand it the thermostat turns on powering the burner. The fan only turns on when it hits the lower limit on the Fan Control Switch (Honeywell Blower limit switch) I think 100 on 150 off - 220 emergency shutdown. My heat exchanger is mounted 8-10 inches above the Fan Control Switch. In my mind with the heat exchanger at 160 the radiant heat may complete the circuit through the Fan Control Switch blowing air all the time. Im having trouble wiring my 24v thermostat to turn on my blower, I have a 24vac Allen Bradley Relay to switch the 110 Vac power, without back feeding my Fan Control Switch. I think if it back feeds it will double feed and kill my blower motor.

Any Ideas?? I can post pics and such if it would help. Your help is greatly appreciated.

[banjoman]

I am not an authority on these by any means but I wrestled with this same thing last year. I was continually trying to control the constant fan on situation electrically. I fixed mine by installing an electrical bypass in the incoming water line. When the thermostat calls for heat, it opens the bypass and water flows through the heat exchanger. When thermostat is satisfied it closes the valve, bypassing water back to the stove. Heat inside the exchanger cools and the fan control is satisfied, turning off the fan.

I do disconnect the bypass valve during the summer eliminating cycling of the valve while using AC.

Hope this helps.

[slimjim]

Not bad Banjoman, here is what I typically do, if you take the thermostat wire and run it into a seperate relay in series with what you already have, on a call for heat the entire cicuit makes and calls everything into operation. The high voltage side of that relay then gets wired ( piggybacked ) to the blower motor, this powers up the blower, now shutting off the burner is easy, simply place an aquastat that breaks on temp rise on the incoming line from the wood boiler, using the R and B terminals on the aquastat run the 2 wires down to the one wire that powers the burner ( B-1 ) cut that wire and attatch the 2 ends to the wires that you just brought over from the aquastat, this will interupt the B-1 circuit whenever the incoming water temp is above the setpoint and complete the circuit whenever the water temp is below setpoint allowing the oil burner to fire on a call for heat. be sure to not cross any wires and always turn off the power before digging in.

[HillBillyEngr]

Thank you both for the help I really appreciate it. I started doodling some ideas today and this is what I think may work pic below. Use a aquastat to control a 110vac relay ( blue). I would wire my current blower system (red) on the Normally Closed Side so when the a-stat had not met then the blower and all that will work as normal. When the A-stat makes then the relay will shift state sending power to the 24v relay (brown) that is controlled by my thermostat. when the heat is called the relay will close and send power to the blower. If the Fan Blower relay has enough heat so that it closes back feeding will not be a problem due to the relay. This look like it will work?? I have both the relays so that will not be a problem or expense.

Another question is how to wire up the 24v relay Im am using W1 as my first stage of heat so would it be W1 on one side and the common wire on the other from the t stat??

Thanks again

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