So I removed my old memco oil boiler and all of the plumbing associated with it so all that I have left is the heat exchanger and the copper runs to the baseboard zones. I'm going to be setting the system up with a primary/secondary design with the outdoor boiler HX integrated into the primary loop. I have 3 heating zones currently and a 4th one planned in the future when I finish my basment.
I'll be using a plate HX for DHW fed off the primary loop with a monoflow tee. My largest zone only has 30' of baseboard. The 2nd zone is about half that and the 3rd zone is one 7' baseboard. All zones are 3/4" copper. The house was setup with zone circulators, but I was debating plumbing it with a variable speed ECM pump and zone valves. I have a bunch of Taco 007 pumps and a controller for up to 6 zones, so I may just end up going that route, but with the low flow requirements I don't want to over pump the zones and end up wasting energy by not having the flow slow enough for efficient heat transfer at the baseboards.
I have a 120k btu oil boiler that will also be plumbed into the primary loop via close tee's, but will only be for a backup system if for some reason I can't run the outdoor boiler. I'll probably set that up to have a constant 120* flow of water through it to avoid cold starting. I won't have that installed right away, just going to be running the G200 and getting the oil setup at some point in the future. I'll try and get a diagram of what I'm planning drawn up in the next few days and posted.