HWBB layout options

mamuel

I had a heatload calculation done and it calls for around 48k btu boiker to replace the old Winkler oil burner. That includes 5k for the basement which I'm unsure of. I attached the 2 layouts of house with current baseboard in red. The 2 boxes in the basement are box/cabinet style emitters. With natural gas running up driveway in spring, I also want to get indirect waterheater to replace old big electric one since might as well if new boiler anyways. A WM CG-3 or Burnham X2 or something will probably be the choices.

Since I have time yet, I was curious on sole options. First floor layout, total fin tube length is around 80ft which i figured was at the end of its effectiveness (70ft?). Current piping jump around and half is hidden by basement ceiling which I'll pull down this spring. I'm not sure if smaller house needs upstairs split in to zones so I'm wondering if 1 zone is priority DWH, can the 2nd zone be split to run parallel both sides of the house? (Green line) splits it evenly at 40ft each side. 1.25 to split 3/4's and return to 1.25 amd water stays hot?

Also basement has HWBB along the rec room which was considered "finished" but still nice cinderblock so not totally insulated but separate and insulated from other half of utility/storage side of basement. Wood burner is currently down there to heat basement and upstairs to save on heating oil. Saving that but disconnecting for new boiler (maybe for garage) and also pellet stove that is not hooked up for rec room area. So I don't think I need baseboard heating in basement unless it can run when upstairs needs heat just to give it some but already asking about out splitting the zone...

While primary secondary piping seems to be the preference, is it required for smaller home and single zones, especially of split so return water isnt cold? Asking to determine pumps vs zone valves and such.