Ive been doing lots of reading , trying to answer my own questions but could sure use some experienced input.
Currently my wood doctor (medium size, 250000 btu, 150 gal ) is serving only my house but I want to add heat to my garage. My set up as it is now : OWF 125 feet from house fed by 1 in. kitek inground. There is a grundfos UP 15-42 at the owf pumping hot water 125 ft into a 20 in x 20 in water to air exchanger in my oil furnace plenum. From there to a 48 in sidearm for dhw and then returns to the boiler thru another 1 in kitek pipe.
My thoughts are this: Id like to add a secondary circuit by adding a pair of Ts at the very end of the return line. I currently have rehau insulated 1in pex buried beside the boiler and running into the building I want to heat. The distance is 20 ft from the boiler to the inside of the building. Once in the building I would take water to the second floor into a Trane water to air unit. My thoughts are to then take the return from the trane to feed my infloor heated slab and from there return to boiler.
I have a 100 gal insulated tank that I can use if the consensus is to keep my boiler water separate from the building water. Perhaps I could just use the new piping from the OWF to heat a sidearm ( or flatplate exchanger) which would then heat the 100 gal tank, and then plumb from the tank in the building to both the infloor and the trane unit upstairs.
I have 2-3 spare grundfos pumps if that factors in.
My current setup as described at first has been running with no issues for 12-13 years. My return temperature to the boiler is only 15-20 degrees colder than the supply, so Im guessing 160-170 degrees. I have not measured this temperature but it feels almost as hot as the supply line beside it.This is what I propose sending to the new secondary circuit.
If you havent realized it yet, I am plumbing challenged but hopefully have explained my setup enough that more knowledgable people can steer me in the right direction.
A couple considerations.... my boiler is nearly level with my furnace plenum in the original primary circuit , only 125 ft away.
Also the slab in the building I want to add heat to is level with the ground the OWB is sitting on. The vertical rise to get water to the trane unit on the second floor is about 16 ft.