Repiping and preparing for new boiler in CI rads 2 unit building

MTC

Hi All,

I have an about 1600 SQ ft up/down duplex with a single old boiler system that I'm assuming was originally gravity fed (2" main trunks, very oversized radiators, etc) that is running on a 1/12HP pump now. I pay the gas bill for the building - no separate gas services and I don't really want to go down that rabbit hole of splitting it.

I'd like to repipe the basement to get the giant piping out of the way for future finished space, as well as to gain some more control over the system. This will include moving the boiler to a new location as well.

I was thinking of installing 2 manifolds with flow meters, one for each apartment, piped to a primary/secondary near boiler system following Dan's schematics in Classic Hydronics. This would allow me to possibly control each apartment separately, or just have the option to split them later be much more convenient. I'm also going to be replacing the basement floor and plan to add loops to the new floor for future finished space down there - I want to set up the system with the ability to add that when the time comes (not immediate). It would be part of the 1st floor unit, not a separate unit, but due to the different heating medium, assuming it will need it's own zone.

SlantFin app heat load came in just under 60k BTU (with very conservative estimations for some things - I think it is probably under 50k in reality), not including the basement expansion. Here's a breakdown of the current radiators:

With my large available radiation, it seems like I could design closer to 140 degrees like an old gravity system than 180 degrees. The system short cycles like crazy with the current 100k output boiler.

Hopefully that is enough context, but please ask any clarifying questions…

What I'm looking to do right now is determine if the 2 manifolds setup is a good plan, and start running piping and setting up the manifolds etc to prepare for a boiler replacement/move in the near future.

Do you think a couple of manifolds setup makes sense? If so, are Bluefin manifolds worth considering (I hear they're identical to Rifeng), considering the dramatically lower cost than Caleffi, Uponor, etc? The building is currently pretty evenly heated, with most of it within a 1-2 degree window - would the flow valves be enough to dial it in reasonably well in this new setup with much smaller basement piping/new boiler location? Would 1/2" hepex or pex-al-pex be sufficient (maybe upsizing for the one giant radiator), or do I need to go larger?

What kind of boiler, separators, etc would you suggest for this setup? My interest is to keep maintenance low, system longevity high, and costs (primarily long term costs, but upfront is always a concern as well) reasonable. Not sure what balance to use of new tech bringing higher efficiency vs simple old setups that are a lot cheaper up front and tend to have less issues/last longer, but higher operating costs...

Pump(s)? The longest run would be about 45 feet of pex each way to connect on to existing 3/4" steel risers that go up one floor (about 10' each way) to the 2nd floor LR rad.

Anything else I'm missing ATM, or suggestions of a different route entirely?

Thanks in advance!

MTC

This is the current rough layout, if it helps. Main trunks are 2", slowly stepping down as you get away from the boiler.

New layout puts the boiler right under the 1st Kit supply/return. I also plan to split the BR rad at right onto it's own loop, then run the bath fintube, followed by basement fintubes, on a separate run - the basement is just to keep the addition area warm enough to not have frozen pipes in the bath above it, and this should be sufficient w/o a separate circuit. This area is slightly colder than the rest of the building, so think that making the bath fintube get full temp water will help balance that better.

The eventual basement additional heated floor zone will be about 3/4 of the main square floor area - all but the bottom right which is a laundry/utilities/storage area that already has a new concrete floor and won't be directly heated. For now, just want to be ready to add this on later w/o changing out controllers and totally repiping the near boiler/main trunks to do it. It likely won't be activated for a few years.