will this work?

Forgive my crude drawings but will this work or is there a better/more efficient way to plumb an add on boiler? I currently have an oil fired boiler in place and will be adding a coal fired boiler onto the system. I want to continue to use my existing domestic water coil that is in my oil boiler. In my mind i could lower the set point on the oil fired boiler (to what i dont know) and let the coal boiler do all of the work. when the circulator pumps kick on it will pull the heated water through the system and both boilers. and the ball valves were intended to give me the ability to isolate the coal boiler from the system if needed. and the upper most ball valve would be in the "open" position only if i were using only the oil boiler.

Tarm USA has everything configured.
http://www.woodboilers.com/admin/upload ... 111Web.pdf
They have done all the homework, with many configurations.
My neighbor runs a Tarm and we followed the guidlines illustrated here.

If you want to continue using the tankless oil in the oil boiler, your proposed setup won't work...think about it, with your piping arrangement the only time heated water flows from the coal boiler to the oil boiler is when one of your zones is calling for heat. You need to circulate between the two boilers if you want to use the tankless in the oil boiler.

Rob R. wrote:If you want to continue using the tankless oil in the oil boiler, your proposed setup won't work...think about it, with your piping arrangement the only time heated water flows from the coal boiler to the oil boiler is when one of your zones is calling for heat. You need to circulate between the two boilers if you want to use the tankless in the oil boiler.

Exactly, you will need a separate pump to do that job. I would also recommend a stack damper on the oil burner to reduce thermal losses up the oil burner's chimney flue if you chose that route.

Ones I have seen when they want to use both, just use the coal boiler to keep the oil boiler hot. That is a circulator loop to oil unit, and then the thermostats still run circulators for house.

coaledsweat wrote:

Rob R. wrote:If you want to continue using the tankless oil in the oil boiler, your proposed setup won't work...think about it, with your piping arrangement the only time heated water flows from the coal boiler to the oil boiler is when one of your zones is calling for heat. You need to circulate between the two boilers if you want to use the tankless in the oil boiler.

Exactly, you will need a separate pump to do that job. I would also recommend a stack damper on the oil burner to reduce thermal losses up the oil burner's chimney flue if you chose that route.

Ones I have seen when they want to use both, just use the coal boiler to keep the oil boiler hot. That is a circulator loop to oil unit, and then the thermostats still run circulators for house

Are the two of you suggesting the same thing? I'm not sure I fuelly understand. Could someone point me to a diagram of this setup? Would you wire the circ pump between the two boilers to run constantly? Or could/would you set it up so that when the t-stat on the oil boiler called for heat it would just start the circ pump that was between the two boilers?

Also, why could you not use a water to water heat exchanger?