I am installing a Kerr TW2000 wood bolier into an existing oil- hot water system. The current system is made up of a Slant/Fin oil boiler with an indirect water tank used for hot water. The zones consist of one containing baseboard heaters and three containing cast iron radiators. All rads(baseboard and cast iron) are plumbed using Wirsbro 1/2 pex pipe so I need to be very careful in my design that these pipes do not overheat. The diagram I am following is attached and is from the manuafacturer. It is a parallel setup with the wood boiler supply being tied into the oil boiler return and the wood boiler return coming from the oil boiler supply. This system seems to keep the oil boiler hot so that it never turns on. I just went to look a a friends system has the same components (infloor radient heating though) but is plumbed much differently. The wood and oil hot water supply are tied together into a mixing valve and sent to the zones and the return are tied together. Totally different. From what I have read, this system is plumbed in series? Is that correct? Whats the advantages and disadvantages of both systems?