I have a Lennox downflow oil furnace. I have just installed a water to air heat exchanger under it from my outdoor wood boiler. I have a Taco 3 way bypass valve in the line so that I can keep heating my domestic hot water. I want to hook up the thermostat so that I am useing the air exchanger for my main heat and oil heat for backup. What thermostat do I need and how should it be wired?
on that domestic water you only move the water when you use it as hot water within the house?if your not running the hot water there is no flow...no heat as first stage heat at the furnace.if you had a circulator as if you had hot water baseboard setup(your add on coil) then the 3-way would have a purpose.if you added a circulator your new stat could move the 3-way for coil heat,and the action in the 3-way valve could have an end switch within it and start the cirulator as first stage heat.the oil burner as 2nd stage could be away from the stat and controlled by a discharge air senser that would keep it off as long as the hot water was satisfying(heating the house)if the air was below the setting the oil would fire up and basically satisfy the stat setting until the next cycle.getting back to your add on coil a klixon would have to be installed on the pipe into it(supply hot water)so when the stat calls the fan won't start till the flow/heat is sensed and blow heated air.....as the oil furnace cycle is..stat...burner...fan.just my thoughts here hope it helps