It seems that this topic has been discussed over and over and over about what connection is right, how best to not loose heat up in the boiler chimney etc over the years, however I have not been able to find any more recent posts about the preferred method of hook up. I picked up a Central Boiler E Classic 1450R at a good price for our 1800sq ft ranch house this weekend. We currently have an older Dunkirk Oil Burner which also heats out DHW as well. My wife is somewhat against the OWB in our current home because it will likely be housed outside and away from the home (not in a wood shed or connected to a garage) however I want to get her used to the OWB route for when we finally move, upgrade to a larger home with a heated garage and heat in the barn etc... So because of this we really want to make sure the heat from the Wood Boiler to the Oil burner is a seamless as possible. A friend of mine is an HVAC contractor and suggested that since this setup and this house is likely temporary to not go insane I will be more than fine to do a direct hook up into my existing boiler connecting the OWB hot water supply to the top of my Dunkirk boiler. Adjust the OWB to 185-190* and lower my indoor boiler temp to around 165-170*. The OWB boiler pump should run continuously. My biggest concern is down time on the OWB. I will have to see how long burn times are on this unit and during the day we typically drop our heat down to 60-62*F and during the time we are home we bring the heat up to 68*F. I will likely have at least 12 hours between a refill of the boiler due to work. Lastly, during hunting season and winter/snowmobile season my wife and I are away from our home quiet often on the weekends. I am concerned about the water in the OWB freezing if there is not fire heating the boiler. My HVAC friend advised I will be more than fine as long as I keep the OWB pump circulating and there shouldn't be any need to run a glycol system and it would likely be very expensive considering the size of the boiler and the likely 50-75' run of thermal pex I will have. I would also be concerned with if I ran a direct system, and the oil burner was running and the OWB was circulating wouldn't my oil burner really suck down oil heating all the 200+ gallons of water running through the OWB as well? If I did a 30% antifreeze system how do I stop this water from mixing with the water in my oil burner for the baseboard heat? I am trying to figure out the proper sizing of the plate heat exchangers but they do not seem terrible priced (depending on size needed) and seems like this may be a better hook up? Having domestic hot water is the other key as well so I need to make sure my oil burner is stay constantly warm. Being that we also recently added natural gas to the house, if it makes things easier, I may down the line just get a stand alone natural gas system and run a heat exchanger from the OWB on that but it just seems like more piping or more work? Anyway sorry for recreating a thread that has been started numerous times, just looking to see if over the years there has been some advancements on hooking both systems up and learning from others experiences. Thanks!